ſº Bº 47 O H44. | 94 | -- ... a. N X2- |TTINUINITINºnº YººHº | ſºlº || ãº) illNilllllllllllllllllll- sº N - º * ~. lºsses º fºLIBRARYºof THE # | Eº * Wºwºw ºº iſ ºn tº W & (s É 2. º É t / 4. As§- ''| d E: C E * Efs šN | º .3%: HºN) y ſº =: §N. "../ , ºr º := [ºr] [º is a ºn 9 É{Rº º ºt:# EºN \ \" wº -ºš *E*.S. - ſ - Sº 2 : És - º, SETH #1 º ... " §º sº. H E. zºº.º. ºn Sº º 5 G E ºvu, º, ºf "...ſº wrºº Jº Jº JAL. J.J. º.º.J.J.J. J. ſº V ºr sº º E * E . . →º-w . . . . . . . … ... . • .* º : ... ." º: * E =3|E - . . . . . . . . . . . . . . . . . . . . . # : E COLLEGE º # : E v º RE […] * Q: OF . # jFij| ENGINEERING ... # #3E º # ăIIITTTTTTTTTTTTTTTIſ: ºffſ[IIITIIITITIIIHIIIſā; ſº B º sº º ºr tº a º ºs º ºs º ºs as a sº a ºn as a º º sº a º ºs º ºs º a º ºs º a sº º sº a º ºs º ºr a • * * * * * * * * ~ * * * ~ * sºn. thrºm M & #72 H 44 | 74 / MAP AND AERIAL PHOTO READING SIMPLIFIED MAP AND AERIAL PHOTO READING SIMPLIFIED * By Lt. Col. W. F. Heavey Corps of Engineers, U. S. Army “Map Reading is in one way like a tourniquet. When you need it, you need it badly.”—MAJOR THOMAS E. STONE in INFANTRY JOURNAL, 1941. T H E M I L IT A R Y S E R VI C E PUBLISHING COMPANY H A R R IS B U R G, P E N N S Y L V A N IA Copyright 1941 by W. F. Heavey 3d Edition, October, 1941 ALL RIGHTS RESERVED KINGENILEDGE ſuſ’ THE MILITARY SERVICE PUBLISHING Co. 100 TELEGRAPH BUILDING HARRISBURG, PA. : ; i : i & The Telegraph Press Harrisburg, Pa. PRINTED IN THE U.S.A. ~~ * -, ~ * TABLE OF CONTENTS Chapter - Page I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 II. Location and Coordinates . . . . . . . . . . . . . . . . . . . . . . 10 III. Distance and Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 IV. Direction and Azimuth . . . . . . . . . . . . . . . . . . . . . . . . 21 V. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 VI. Elevation and Relief . . . . . . . . . . . . . . . . . . . . . . . . . . 37 VII. Map Reading in the Field . . . . . . . . . . . . . . . . . . . . 49 VIII. Reading Aerial Photographs . . . . . . . . . . . . . . . . . . . 55 IX. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 CHAPTER I INTRODUCTION 1. Importance. The ability to read a map is of the greatest importance to practically all officers and noncommissioned officers. Through study of the map the higher commander arrives at his tactical decision. By means of the map he transmits the orders which outline his plans to the subordinate commanders. These subordinate commanders must be able to read the map if they are to understand these orders and the specific part they have been ordered to accomplish. By using the map the various units of the combat teams move to their allotted positions, identify their areas, boundaries, and objectives, and conduct and report their subsequent operations. The map is also an important source of data for the delivery of aerial bombing and artillery, machine gun, and other supporting fires. From the junior non- commissioned officer to the senior general, the map will be a weapon often as indispensable as the rifle to the rifleman. Because of the increasing use of aerial photos as maps or in connection therewith, a considerable portion of this text is devoted to the elementary reading of aerial photos and to their use in tactical operations. 2. General. The military terrain consists of various features which may be considered as favorable or unfavorable to an operation, depending upon whether they tend to facilitate or to hamper our activities or those of the enemy. To be able to recognize these features and properly to evaluate them is a problem confronting tactical commanders. Other things being equal, the commander who best recognizes these features and utilizes them the most skillfully (exploits the favorable, and circumvents the unfavorable) has thereby an advantage, often the deciding advantage. The tendency today is toward wider fronts and greater depths. Motorization and mechanization make wider and faster movements possible. The commander of tomorrow will have more terrain to learn and less time in which to study it. Personal reconnaissance may be impracticable because of the great areas involved and the lack of time. Thus the knowledge of the terrain upon which plans are based will frequently be limited to that which can be secured from maps. The ability to read maps accurately, rapidly, and skillfully has become a most necessary attribute to the successful tactical commander. There is nothing difficult about map reading. Unfortunately, however, maps will be read in battle, often when hands are numb and clumsy from wet and cold; when mind and body are dulled by fatigue and exhaustion; read in an environment of noise, confusion, and excitement and frequently in great 1 2 MAP AND AERIAL PHOTO READING haste. These conditions are a fertile field for errors. Errors in map reading may be very costly. There must be no such errors. The only assurance against them is knowledge of the essential operations of map reading, so thoroughly understood and deeply rooted by practice that their performance is automatic. 3. Purpose of This Text. Map reading is not difficult once the basic con- struction of the map is understood. The purpose of this text is to present the subject so that the student, regardless of previous educational qualifications, may with reasonable effort become not only a proficient but also a quick and accurate reader of maps. It is the purpose of the author to present the one simplest method of accomplishing each task; alternate methods will be omitted for reasons of brevity. At the end of most of the chapters are given practical questions and problems for the student to solve. Students are urged to solve these problems independently. Solutions are included in the Appendix for use in checking the student's work. CONVENTIONAL SIGNS SHOWN ON PLATE 1. Numerical Key . Good motor road, paved. . Telephone or telegraph line. Double track standard gauge railroad. Stream or creek (blue on a four-color map). Fence, Smooth Wire. . Triangulation point or primary traverse sta- OIl. . Corn field. . Fence, barbed Wire. . Tall tropical grass. . River (blue on a four-color map.) . Woodland (deciduous trees.) . LOne trees. . Buildings in general. . Orchard. . Railroad crossing, highway over railroad. . Fence of any kind. . Schoolhouse. . Cultivated field, Sugar Cane. . Grass-land. Dam. . Electric power transmission line. . Church. . Cemetery. . City, town or village. . Bridge, suspension. . Railroad crossing, railroad above. 27. Fill Bridge, steel (S). . Cut, railroad. . Bridge, truss or girder, for standard gauge RR, . Narrow-gauge railroad. . Bridge, highway, general . Railroad, single track, standard gauge. . Mine or quarry of any kind (or open cut). . Accentuated (every fifth) contour. . Wire entanglement. . Low or portable entanglement. . Trenches (dotted when proposed). . Demolitions (Ruins). . Ford, general symbol for vehicle ford. . Good pack trail or foot path. . Bridge, foot. . City, town or village (generalized). . Intermittent Stream. . Worm fence. . Stone fence. . Tank trap. . Equestrian ford. . Road, poor motor, unpaved. . Marsh. . Head of small stream. . Bench mark, Elev. 555 ft. Alphabetical Key Bench mark . . . . . . . º e º 'º - Bridge, foot Bridge, highway, general .................. Bridge, highway, made of steel (S) . . . . . . © - Bridge, truss, or girder ................... Q Bridge, suspension ....... © 6 & © tº e º e º e Buildings in general . . . . . . . . . . . . . . . . . . . . gº tº º º City, town or village (generalized) ........ Combination showing city, town or village Crossing, railroad (RR above) .............. Crossing, railroad (RR beneath) Cemetery • * * * * * * * * * * * * * e º º e & * * * * * * * * * * e º 'º e º e º e & G e º O e º e º is * * * * * * * * * > * * * * > * tº e º e º e Cut e e º e º 'º e º e º e s tº e º º • e º 'º - e º e º e º e tº e º 'º e º º tº º Dann * * * * * * * * c e º e s e © e º e º º c e º ºs e g º e º 'º tº º O & © tº gº e º 'º Demolitions (ruins) . . . . . . . . . . . tº e º 'º e º e º ºs tº e - e. Electric power transmission line . . . . . . . . . . Fence of any kind (or board fence) Fence, barbed wire Fence, Smooth Wire Fence, Stone Fence, Fill s e e o e º e º e s e e º 'º e e s e e s e e e e tº º e º ºs e tº • ‘º e º ºs e º e º 'º Ford, equestrian . . . . . . . . . . . . e e º e º e e º e º e s e s e e Ford, for vehicles Grass-land e tº e º g º ºs • * * * * * * * * * * c e s e e e s e e o e o e e e Grass, tall tropical . . . . . . tº e º e s e e º 'º e © & © e º tº e - Marsh e e º 'º e º e g º e º 'º e - e. e. e. e. e. e. e. © & © & © e º 'º u ę. e. e. e. e. e. e. g. Mine or quarry of any kind (or open cut) Orchard Pasture Or grass-land e tº e º e º e º e * * @ 9 e º e º & e © º Railroad, double track, standard gauge . . Railroad, narrow gauge .................... Railroad, single track, standard gauge .... River (blue on a four-color map) Road, good motor, paved . . . . . . . . . . . . . . . . . . Road, poor motor, unpaved Schoolhouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stream or creek, intermittent . . . . . . . . . . . . Stream or creek, perennial (blue on a four- Color map) . . . . . . . . . . . . . . . . . . . . tº º º e º e º e º e º Stream, head of Tank trap Telephone or telegraph line Trail or foot path Trees, lone Trees, deciduous Trenches (dotted when proposed) Triangulation point or primary traverse Station e e º e º 'º e - © e ∈ E e º 'º - e º 'º e º 'º e º Q & © e º e e tº e º 'º Wire entanglement . . . . . . . . . . . . . . . . . . . . . . . . . Wire entanglement (low or portable) . . . . . . Woodland (deciduous trees) & © tº e º G & º & e º ºs e e o 0 & • * * * tº e ºs e e tº º e º ſº tº º º © º º ºs e e º 'º tº e º e º e º ſº tº • * * @ & © e º 'º - e. e e º º s e º e s tº e º e º ºs e º 'º e º & © e º e º e INTRODUCTION 4O .ſº Ēfi 3 3; Šºſ © o $2 ** ! ， º tº e º £ € © © îș € £ © ® sę tº Q， Q， \，= \， \，= \， \！º ſº ſº gº tº tº @ :§ 4º & º ſº º ſe ſ-a \，= \，`<`_3 \;=£ €= ！--�~→ »©3 † - - - - + + + +|ș: ��� t- ſ- e- t- ſ- ſº ſ- ſ-Š {*<！-- tº ſº t- ſ- ſ- ſº|ºj C) v) g| © ×)O } 5% � zë44||žij�} ºffi șiCN {§3;;;;;;;;•}}�� O Ēſt OOŁ 19 18 uſ) <！=） Plate 1. Conventional Signs. 4 MAP AND AERIAL PHOTO READING 4. Qualifications. To qualify as a satisfactory reader of a map, the student should be able to do the following: a. To designate the location of a point on the map by the use of coordinates. b. To determine the distance and direction from one point to another desig- nated point. c. To determine whether one point is higher than another and, if so, by how much. d. To find out whether an observer can see a distant point over an intervening ridge. e. Finally, by his knowledge of conventional signs used on the map (especi- ally contours), to visualize the terrain with all its natural and man-made features. This qualification reaches its ultimate when the map reader visual- izes from the map not a collection of brown contour lines (form lines each at the same elevation), black roads, blue stream lines, and green woods lines, but a miniature replica of the ground itself with its drainage system, its hills and valleys and wooded areas, together with the works of man such as roads, houses, and crops. The scope of this text is limited to the essential qualifications listed above. The student who masters these simple rudiments can feel assured that he has the information necessary for an intelligent use of military maps. 5. Conventional Signs. The student knows from his geography that certain signs are used on maps to represent various features. Dots or small circles represent towns or cities; wavy lines represent rivers; other lines represent boundaries. These signs adopted through custom are known as “conventional signs.” Military maps are intended to show detailed information and there- fore contain many more conventional signs than the maps in geographies. These signs have been standardized for the military service and are published in Basic Field Manual 21-30. Usually they picture or suggest the feature that they represent. The map shown in Plate 1 contains most of the ordinary conventional signs. The student should study these signs, referring to the numerical key on the opposite page to verify his interpretation of each feature. To increase their value, the standard maps (see Special Map A in envelope in back of this text) are printed in four colors, as follows: a. Black for the works of man, for names, and for grids. b. Blue for water. c. Green for woods and vegetation. d. Brown for contours. Certain maps use a fifth color, red, to show important highways and railways, INTRODUCTION 5 6. Interpretation of Conventional Signs. In actual practice conventional signs must not be accepted too literally. In the first place, the works of man may have changed since the map was made. A trail may have been rebuilt and is now a road; a ford may have been replaced by a bridge, or it may have been washed out altogether since the map maker checked its condition. Timely and thorough investigation by reconnaissance (both aerial and terres- trial if possible) should always be made. The necessity for this verification cannot be more strongly emphasized than by citing an actual incident of one of the British columns landing last year in Norway. The British commander pushed his force up one of the deep valleys until he met contact with Ger. mans advancing from the south. Studying his map, he noted there was indicated a trail leading from in rear of the German position over a high mountain range to a locality well in rear of the British. Questioning friendly Norwegians, regarding the trail, he was told “just a trail, not passable to trucks, full of snow anyhow.” So the British commander took no further action, made no reconnaissance. On the other hand the German commander had a thorough reconnaissance made. He discovered that with work at several defiles by his engineers, the “trail” could quickly be made passable even though very rough. A few days later German mechanized forces made a surprise attack from the “trail” on the British rear. The “trail” had become a road. 7. Military Symbols. In addition to conventional signs, a special class of signs known as military symbols has been developed to represent the various tactical units such as platoons, companies, battalions, and regiments, as well as installations such as command posts, first aid stations, lines of departure, and ammunition distributing points. The standardized military symbols are also included in Basic Field Manual 21-30, to which reference has been made. Plate 2 lists the military symbols most frequently used. By means of these symbols the size, identity, and designation of the various units and installations, the location and type of supporting weapons, and the necessary lines and boundaries for an operation may be graphically indicated. In no field of life is the Chinese adage that “one picture is worth ten thousand words” more applicable than in the use in military operations of the map with its conventional signs and military symbols. A map with the operation outlined thereon truly saves many a thousand words in orders. The student should practice making the symbols used for his unit and for those with which he is associated. These symbols must be learned. The follow- ing general rules should assist in remembering them: a. Units or installations in territory occupied by our forces are usually shown in blue; those in enemy territory in red. 6 MAP AND AERIAL PHOTO READING Military post or station; coni- mand post or headquarters. . (Lower end of staff or sym- bol will terminate at point Of establishment, repre- sented.) Troop unit. . . . . . . . . . . . . . . . . . . . . Observation post Supply depot Supply point tº e g g tº º gº tº gº & Cº º tº © e º e e Supply train or transportation unit; Animal-drawn . . . . . . . . dº º e º 'º º Motor-drawn or motorized. . Pack Railway e tº ſº sº e º º º © tº e º 'º e º 'º e º & 6 ſº tº º º tº e º ºs e º & e º e º e º 'º e g º g g is Branch of Service. (Usually placed inside of basic symbols shown above) Air Corps . . . . . Airship e e s a dº e º o e º e e º e º e s = e º s e e s & Armored Force . . . . . . . . . . . . . . . . . (When used with any arm or service symbol indicates mech- anized unit.) Artillery & © tº e º ſº tº tº e º 'º tº º e º te & e º & G & º & Cavalry, horse and mechanized Chemical Warfare Service tº º tº ſº tº Engineers * * * * * * * * * * * * * * g e º g º e º e Infantry . . . . . . . . . . . . tº e º e g º ºs e º e & Infantry, motorized Infantry, parachute Military police . . . . . . © e s e º 'º e º e Medical Department tº ſº e º 'º - a s gº tº & © tº dº y & 4 e º 'º º Ordnance Department Ammunition © º ºs º w tº º ſº e {..} & © tº ſº tº gº tº e g g ſº tº e s tº g tº e g g g g º ºs e g tº 4 g & Prisoners of War s & a s & s sº e º & Quartermaster Corps Class I Supplies Gasoline and Oil only e e º e º 'º e º e º p & e < * * e º 'º Signal Corps tº e º e º e Signal Corps, Aviation Size of Units. (Usually placed above basic sym- bols shown above, or in boundaries shown below.) Squad Section . . . . . . . . . . . . . . . . . . . . . . * e s Platoon . . . . . . . . . . . . . . . . . . . . . . . . . Company Battalion tº dº e º & tº ſº e º ºs g º ºs & e º $ $ tº & tº e º is tº $ e g º e e º 'º e º 'º gº tº e º e º e º 'º e e º gº k ; zº- ; Gun bat- tery HOWitzer mortar Howitzer mortar battery © tº gº e º e e Or Or Regiment . . . . . . . . . . . . . . . . . . . . . . . Brigade . . . . . . . . . . . . . . . . . . . . . . . . . Division . . . . . . . . . . . . . . . . . . . . . . . . Corps . . . . . . . . . . . . . . . . . . . . . . . . . . . Army . . . . . & © e g º ſº tº e tº º e º gº tº gº tº e º ſº g g is General Headquarters . . . . . . . . . Boundaries. Squad . . . . . . . . . . . . . . . . . . . . . . . . . Section . . . . . . . . . . . . . . . . . . . . . tº e o s Platoon . . . . . . . . . . . . . . . . . . . . . . . Company . . . . . . . . . . . . . . . . . . . . . . Battalion . . . . . . . . . . . . . . . . . . . . . . . Regiment . . . . . . . . . . . . . . . . . . . . . . Brigade . . . . . . . . . . . . . . . . . . . . tº e > * > Division . . . . . . . . . . . . ., * * * * * * * * * * * Front line . . . . . . . . . . . . . . . . . . . . . . Limit of Wheeled traffic, day . . Limit of wheeled traffic, night. . Straggler line . . . . . . . . . . . . . . . . . . Miscellaneous. Antitank gun (Specify caliber.) Antitank gun in position, prin- cipal direction of fire . . . . . Antitank gun emplacement with principal direction tº gº e g & e º 'º e Area to be gassed, nonpersistent Area to be gassed, persistent .. Automatic rifle . . . . . . . . . . . . . . . . (Dotted When emplacement is not occupied, thus) . . . . . . . Barrage (Size indicates extent and notation, type) : : (Blue) (Blue) § T. [º] Machine gun. © tº e º is e º ſº dº ſº tº e º e º 'º e sº O-º-º- (Arrow to point in principal direction of fire. When used alone it indicates ma- Chine gun, Water-cooled, cal. .30.) Machine-gun symbol under symbol of unit of any arm indicates machine-gun unit of that arm.) Antiaircraft . . . . . . . . . . . . . . . ... •-ºr-º- Antitank . . . . . . * @ & & e s sº sº gº g ..... e-FF-> Caliber .50 . . . . . tº º º & © e º e e e º gº º e 5O Light . . . . . . . . . . . . . . . . . . . . . . . . . Open when em- placement is unoccupied, { thus . . . . . . . . . +} º 37-mm gun . . . . . . . . . . . . . & © e g g º e & $ 37-mm 81-mm mortar . . . . . . . . . . tº gº e º ºs e tº -- 81-mm 4.2” chemical mortar . . . . . . . . . . -º- º: cml e * Machine gun (Single gun) Cº-º-º-º- (Arrows to indicate sectors of fire; Shaded portion to show danger space when fire is placed in final protective line.) 37 O 2^ Machine-gun section (two guns) *** %3% Normal barrage, machine guns. . 2 Message Center . . . . . . . . . . . . . . . . . Ms% Cen Mines, individual, layOut Or area included shown to scale. . Qor Obstacle, individual . . . . . . . . . . . . X Obstacle, bridge out . . . . . . . . . . ) }% ( Road block . . . . . . . . ë e º ºs º e º e g º ºs % Switching control at COmlmand F post . . . . . . . . . . . . . . . . . . . . . . . . Tank trap 4:"> isºme,” “… ** One-Way . . . . . . . . . . . . . . . . . . . . . ->-º- Two-Way . . . . . . . . . . . . . . . . . . . . . ><->-6 Application of Symbols. The following examples show the use of Special Symbols as applied to Various military Organizations or activities. They are in- tended to illustrate the method of combining basic symbols and abbreviations to show the desired information and are only a few of the possible combinations. (1) Air Corps. Pé. 701st Air Base Squadron . . . . . . 7 Oſ tº tº 9 & É3 7 obsn ſºil 88th Reconnaissance Squadron E3’ss º 1st Staff Squadron . . . . . . . . . . . . E3 i Stf Headquarters and Headquarters Squadron, GHQ Air Force. . [ääJar 901st Transport Squadron 7th Observation Squadron 101st Balloon Squadron. . . . . . . . § 10 3d Air Force . . . . . . . . . . . . . . . . . . . . É3Af 701st Bombardment Wing . . . . . . Eäzo Bomb(L) (Light, medium, heavy) 532d Pursuit Group (interceptor) Éss2 Por (I) (or fighter) 203d School Squadron . . . . . . . . . Gä20s sch (2) Cavalry. Light; Machine-Gun Troop A, 2d Cavalry . . . . . . . Platoon, e Gº & AD212 o-E-> Transportation Platoon, Head- tº e º quarters Troop, 2d Cavalry. . Hqſº, 2 Scout Car Platoon, 2d Cavalry. . seteſ#2 1st Platoon, Special Weapons e C & Troop, 14th Cavalry ....... 1 SPWPnſzºl-4 1st Platoon, Antitank Troop, * ... 1st cavalry Division ........ 1 ATIZ11 Div C & O 1st Platoon, Troop A, 4th Cav- alry, Horse and Mechanized 1 A 214 261 ºn', Troop G (Motor- e & © cycle), 4th Cavalry, Horse and Mechanized 2 G|Z 4. IHeadquarters Troop, 8th Cavalry e #. & e º 'º & & º & ſº dº ſº tº e < * * * * is s s HQ. Ca 8 brig ph 7 L1: •–42-- *Dål, Troop A, 1st Reconnaissance Squadron . . . . . . . . . . . . . . . . . . *[H] "ren Special Weapons Troop, 3d Cavalry . . . . . . . . . . . . . . . . . . . . . Sp W Lº 3. Troop F, 2d Cavalry . . . . . . . . . . E[16 Troop E (Scout Car), 6th Cav- alry, Horse and Mechanized Reconnaissance Troop (Mechan- ized), 9th Division . . . . . . . . Renſä19 II:#1, Machine-Gun Troop, 7th Cavalry Machine-Gun Troop, Caliber .50, 2d Cavalry . . . . . . . . . . . . . . . . . 1st Squadron, 1st Cavalry (mechanized) . . . . . . . . . . . . . . 1st Squadron, 4th Cavalry 1 ſº 4. 18th Cavalry . . . . . . . . . . . . tº e º e it is e tº 18 1st Cavalry Brigade . . . . . . . . . . . tº 4th Cavalry Division . . . . . . . . . . [14 Command Post, 5th Cavalry 5 Brigade . . . . . . . . . . . . . . . . . . . . .-1!!..." Park, Mechanized Units of Horse { ;Prix Cavalry Regiment . . . . . . . . . * * * * * * (3) Chemical Warfare Service. COmpany C, 901st Chemical Regiment . . . . . . . . . . . . . . . . . . C (#) 9 Ol 2d Battalion, 901st Chemical Regiment. . . . . . . . . . . . . . . . . . . 2 [3] 90 (4) Coast Artillery Corps. [;]ssbar Balloon Barrage Battalion . . . . . 2d Battalion, 2d Coast Artillery, 2[*]2H-D Harbor Defense . . . . . . . . . . . . Searchlight Platoon, Battery A. *[Z-N104 104th Coast Artillery (AA). . & Machine-Gun Platoon, Battery © e & E, 104th Coast Artillery eſ: iO4 (AA) . . . . . . . . . . . . . . . . . . . . . . . ©-dº. 37-mm Platoon, Batterv F. 104th FLZSJ104 Coast Artillery (AA) . . . . . . . ë * * * * * * * tº e s tº e º e º 'º & © tº ºn tº it & * * * * * * e º 'º e º e s tº e º ſº tº e s e s & 1st Battalion, 104th Coast Artil- lery (AA) . . . . . . . . . . . . . . . . . . . 'Lºlios 2d Battalion, 104th Coast Artil- *L*Sloa lery (AA) . . . . . . . . .. . . . . . . . . . . •—tº- 77th Separate Coast Artillery Battalion (AA, 37-mm) . . . . 104th Coast Artillery (AA) . . . . Cºlios 912th Coast Artillery, Railway.. 912 Ry 57th Coast Artillery, 155-mm [**157ca Gun . . . . . . . . . . . . . . . . . . . . . . . . & 155 (5) Corps of Engineers. Company A, 2d Engineers (com- º * * > *g º & & e º 'º e º e s e º e º 'º e º e º e A [E 2 77 Sep © 37 15th Engineer Squadron ... . . . . [h 15 302d Engineer Battalion (sepa- rate) ſé, 302 sep 301st Engineers-, (general service) [*20. gen serv 905th.ºrs (heavy ponton. [H]905hypon mtz motorized) . . . . . . . . . . . . . . . . . 801st Engineers (water supply) [É180 w Sup XX Engineer dump, 5th division . . {E} 5 12th Engineer Battalion (Tri- $º angular Division) . . . . . . . . . . [ÉJ12 2d Platoon, 70th Engineers, Light Ponton, Motorized, GBHQ Re- SëTVē . . . . . . . . . . * * * g e º ſº tº e º e º tº 2[...]zol Pon GHQ Bridge Company, 16th Engineer Battalion Armored . . . . . . . . . . Br[Þ16 2d Platoon, Company B, 28th © tº gº *-*. Engineers (Aviation) . . . . . . 2 B [E]28Avn XX Engineer Park, II Corps . . . . . . . . (EII Engineer Depot No. 2, First XXXX ë º, ºpe, Nº. 4 tº Żë First (6) Field Artillery. Battery F, 2d Field Artillery . . F[#12 (This symbol may be used to show artillery position area.) Combat Train, 2d Battalion, 3d Field Artillery . . . . . . . . . . . . . cTN 2 ... 3 Headquarters Battery, 2d Bat- talion, 4th Field Artillery ... Ho 2 [t] 4 Battery A, 3d Ammunition Train A [...] 3 1st Battalion, 8th Field Artillery iſ: 8 951st Field Artillery Battalion (mechanized) . . . . . . . . . . . . . . [ć] 951 1st Ammunition Train . . . . . . . . [...] I 21st Field Artillery (horse) . . . . ſº 2| 103d Field Artillery (155-mm gun] . . . . . . . . . . . . . . . . . . . . . . . fºlloššniss m rin 101st Field Artillery (155-mm howitzer) . . . . . . . . . . . . . . . . . . . [*] jQI F2w. 155 mm Command Post, 8th Field Artil- lery . . . . . . . . . . . . . . . . . . . . . . . . . F. 8 bservation Post, 3d Battalion, O *ś *...* * 3 Å 2O3 Gasoline Section, Service Bat- tery, 54th Field Artillery Regiment (105-mm Howitzer © & —Armored) . . . . . . . . . . . . . . . . . YServiſºjš4 2d Section, Battery B, 71st Fioli -à-IO 5 Artillery Battalion, Horse- drawn . . . . . . . . . . . . . . . . . . . . . . 2B f: 7| (H Dr) Headquarters Battery, 1st Divi- e sion Artillery (Triangular) . . HQE] Div (7) Infantry. The Infantry Company. Rifle Co. A (B) (C) (E) (F) (G) (I) (K) (L) (29th Inf.) . . . *Cºlis Headquarters Platoon (Co. A ( Q @ 29th Inf.) . . . . . . . . . . . . . . . . . . HQADS329 60-mm Mortar Section (Co. A Q Q 29th Inf.) . . . . . . . . . . . . . . . . . ADS329 60-mm Mortar Squads 1st (2d) + (CO. A 29th Inf.) . . . . . . . . . . iAS329 Light Machine Gun Section (Co. :*: A 29th Inf.) . . . . . . . . . . . . . . . . Ašº's 6-lº- Light Machine Gun Squads 1st (2d) (Co. A 29th Inf.) . . . . . . 1sº Rifle Platoon 1st (2d) (3d) (Co. A 29th Inf.) ..... tº º ſº a tº ſº e º º & *jºgº º ( O (Co. A 29th Inf.) . . . . . . . . . . iAS329 The Infantry Company, Heavy DE329 & Q O iAC329 Weapons Co. D (H) (M) (29th Inf.) . . . . . . . . . . . . . . . . . Heavy Machine Gun Platoons 1st C O © Čš. Dºñº.”... iDC329 O-º- Herº, * Sections § © () ) th) (Co. D 29th Inf.) iDES329 O-º- Heavy Machine Gun Squads 1st O (2d) (3d) (4th) (5th) (6th) 2. §) ºth)'''é. Isºn º id-129 Caliber .50 Machine Gun Platoon O O O (Co. D 29th Inf.) . . . . . tº e º & tº Caliber .50 Machine Gun Squads O iš Čá)” ºf 23; ºº idS329 C-30- 81-mm Mortar Platoon (CO. D O © O 29th Inf.) . . . . . . . . . . . . . . . . . . DC329 81-mm Mortar Squads 1st (2d) + (Co. D 29th Inf.) . . . . . . . . . . iDS329 -º- 1st Antitank Squad, Antitank O Company, 1st Infantry 1ATC- Weapons Platoon, Company E, • C & 6th Infantry, Armored . . . . . wºn EEJó 3d Platoon, 205th Military Police tº e & Company . . . . . . . . . . . . . . . . . . . 3DME 2O5 501st Infantry Battalion (Para- chute) . . . . . . . . . . . . . . . . . . . . . . Ekso (ºrd) 8th Infantry (Motorized) . . . . . Bºls Mtz. XX 8th Division . . . . . . * @ e is © & & © tº gº as e e D3/8 Command Post, 3d Battalion, 4th Infantry . . . . . . . . . . . . . . . 3 Hºl. | 1 || Observation POSt, 6th Infantry. 6 1st Infantry Train . . . . . . . . . . . . . jº Medical Detachment, 29th In- fantry . . . . . . . . . . . . . . . . . . . . . . DETEE29 Inf 1st Battalion Section, Medical & O Detachment, 29th Infantry 1B,BE29 Inf Aid Station, 1st Battalion, 29th Infantry . . . . . . . . . . . . . . . . . . . . 1 L129Inf Headquarters, Medical Detach- ment, 29th Infantry . . . . . . . . Diff=29 of (8) Armored Force. Headquarters Company, 1st Armored Division . . . . . . . . . . Ell Di IV Military Police Platoon, Head- H4 quarters Company, 1st Ar- mored Division . . . . . . . . . . . . MP [äji Div Transportation Platoon, Head- Quarters Company, 1st Ar- mored Division . . . . . . . . . . . . . T Hiſè. 1 Div 1st Reconnaissance Battalion .. Rifle Company, 1st Reconnais- [+]1 Ron Sance Battalion . . . . . . . . . . . . DEl Ren Weapons Platoon, 1st Recon- Inaissance Battalion . . . . . . . . © º Ch Motorcycle Platoon, 1st Recon- wDE1R naissance Battalion . . . . . . . . [É jR Cn Armored Company (L), 1st Re- MtcIA COnnaissance Battalion . . . . cE1 Rcn 1st Armored Brigade . . . . . . . . * * [æ], INTRODUCTION 9 Communications Platoon, Head- quarters Company 1st Ar- Com H4E11 Brig Company E (ambulance), 101st • ‘autºBlo. mored Brigade . . . . . . . . . . . . . . Medical Regiment . . . . . . . . . Headquarters Company, 1st Company G (hospital), 3d Medi- Armored Regiment (L) . . . . Ha [º]1(L) cal Regiment . . . . . . . . . . . . . . . coloshtās Maintenance Piatoon, Service 101st Veterinary Company . . . . . NZ or Company, 1st Armored Regi-. A., . e O © ment (L) . . . . . . . . . . . . . . . . . . Meinſ Serv[eſ]1(1) Troop A (collecting), 1st Medi- $ cal Squadron . . . . . . . . . . . . . . A colº ! Reconnaissance Company, 1st E] Armored Regiment (L) .... Rcn 1 (L) Troop B (ambulance), 1st Medi- • AutºHº Machine Gun Company, 1st Ar- [E]. (L) cal Squadron . . . . . . . . . . . . . . In Ored Regiment (L) tº ſº tº e e º sº. e-º- Troop C (hospital), 1st, Medical coloshH. Company A, 1st Armored Regi- A [E]1(L) Squadron * * * * e º ºs e º s e º a e º 'º e º a ment (L.) . . . . . . . . . . . . . . . . . . Veterinary Troop, 1st Medical Cºl. 69th Armored Regiment (M) . . Élé9 (M) 1st, sº. tº e s is s is a e º e e a º e e º e º a attalion (collecting), 1st * - .….................. 2d Battalion (anbulance), 1st ić (9) Medical Department. Medical Regiment ... . . . . . . . 2 (AMB) H- Service Company, 1st Medical 3d Battalion (hospital), 101st $. Regiment ... . . . . . . . . . . stavÉ. Medical Regiment . . . . . . . . . . stºoshāo Company A (collecting), 1st 3. à. Medical Regiment . . . . . . . . . . A colòB. 1st Medical Squadron . . . . . . . . . . Comº f (ambulance, animal- *Optional. raWn), 501st Ambulance Yº: Battalion . . . . . . . . . . . . . . . . . . . U ows EH 30 Plate 2. Special Military Symbols. b. In designating units: (1) Numbers of divisions, regiments, and separate battalions or com- panies are placed on the right. (2) Numbers designating battalions within a regiment are shown on the left. (3) Letters designating companies, troops, or batteries are shown on the left, always in capitals. - (4) Calibers of weapons are shown by numbers and unit of measure, as 37-mm. Exceptions are that the caliber of the caliber 50 machine gun is indi- cated solely by the number 50, and the figure 30 is not employed with either heavy or light caliber 30 machine guns, the caliber of these weapons being understood. * CHAPTER II LOCATION AND COORDINATES 8. Use of Names and Numbers. The most suitable method of designating a feature on a map is by a name or number. The names of cities, towns, lakes, rivers, mountains, woods, and similar features and the numbers of federal, state, and county highways are invariably shown on topographic maps. Military maps endeavor to show the names or numbers of all locally known features to facilitate their identification and location in the field. Hills, road junctions, and crossroads are often given numbers, usually their elevation above sea level, thus serving the dual purpose of designating the feature and of conveying information as to the local topography through the elevation number. How- ever, if all features of military value on a map were numbered or named, the map would become a maze of names and figures. For that reason the use of coordinates has been adopted for military maps. There are two types of co- ordinates with which the student must become familiar, polar coordinates and grid (rectangular) coordinates. 9. Location. By Polar Coordinates. This system consists in locating a feature by giving its distance and direction from a nearby feature which is named. 3 *—a –1–1–4–A.—a A-4. Tr w y- &i . y s . º: :. 32 * * F. !---xC }= 3| 3. a a - a a a A-a_a_A. s l O | || 12 J3 14 15 Plate 3. Grid System. Thus (see Plate 1), it is only necessary to say, “Road junction one-half mile south of MILLDALE” or “Tank trap one-half mile east of H. J. COLLINS” to identify the features in question. For greater accuracy the distance may be accurately measured in yards and the direction given in degrees. 10. The Grid System. To understand the grid system, assume that Plate 3 represents a map on which the topographical features have been omitted. Draw 10 LOCATION AND COORDINATES 11 on this map a series of parallel lines in a north-south direction at, say, the map distance of 1000 yards apart. Then draw a similar series but on an east and west direction. Our map has now been divided into a series of squares called “grids.” The lower left-hand grid corner is taken as origin, and the lines are numbered consecutively from east to west in one series and from south to north in another series. The vertical (north and south) lines are the Y lines; the horizontal (east and west) lines are the X lines. 11. Location By Grid Square. The distance of any point east of the origin is called the X coordinate; the distance north of the origin the Y coordinate. The X coordinate (left to right) is always read first. A dash is placed between the X and Y coordinates and the whole inclosed within parentheses. Thus the 842 843 844. | 4 || 4 - |-ºz –9 | 4 || 3 | § § # § * § Ž ! | 4 || 2 Plate 4. Using the “L” Shaped Coordinate Card. The coordinates of point “P” are (43.63–13.77). coordinates of Point A (Plate 3) are (13–31). Any grid square can be indicated by giving the numbers of the two grid lines at its lower left (S.W.) corner. To indicate features on a map, much time is saved by simply designating the grid square in which the feature will be found. Thus, Point B (Plate 3) is in grid 12 MAP AND AERIAL PHOTO READING square (12–32). This reduces the searching for the feature to an area 1000 yards Square. * 12. Location By Grid Coordinates. Often it is necessary to indicate the exact location of a feature such as a machine-gun emplacement. This is done by indicating its exact position within the proper grid square. For example, Point B (Plate 3) is four-tenths of the horizontal distance across the grid square in which it is located and five-tenths of the vertical distance. Its grid coordi- 842 843 84.4 |4|4 8-| p GRID CARD |4-13 |4|2 Plate 5. Using the Rectangular Coordinate Card. The coordinates of the point “P” are (43.63 — 1377). nates would therefore be (12:4-32.5). The left to right (the horizontal) read- ing is always stated first. Beginners often make the error of reading the wrong coordinate first. This error can be avoided by remembering either of two rules of thumb. One is to remember the key phrase, “READ RIGHT UP;” the other is to remember the letters HV, meaning to read the horizontal LOCATION AND COORDINATES * 13 distance first and then the vertical. Since the ordinary grid square measures 1000 yards on a side, a reading to tenths (one decimal) gives a location to the nearest 100 yards. A reading to hundredths (two decimals) gives an accuracy within 10 yards. For example, the coordinates of Point C (Plate 3) to the nearest 10 yards would be (1135-3150). When the grid numbers have more than two digits, it is customary to drop all but the last two digits. It is also customary to use the same number of decimals with both coordinates even though one of them ends in zero. 13. The Coordinate Card. The reading or plotting of grid coordinates is greatly facilitated by the use of the coordinate card. This card is, in effect, a 64O 645 29O 5—B E 4–= O E 3—E Tº P 2—E |:62,500 i 1–3 E 5. 4. 3 2 | - 285 huluulu huluuluuluuluuluu 111F 64O G45 Plate 6. Reading Coordinates on the 5000-Yard Grid. The coordinates of point “P” are (43.7–873). double scale that can be placed on the map and by means of which both the horizontal and the vertical interpolations can be made at one time. There are two types of coordinate cards in general use. One of them is “L” shaped, and the other is rectangular or square. The manner of using the cards is similar and 14 MAP AND AERIAL PHOTO READING is shown in Plates 4 and 5. Graduated coordinate cards are included on the protractors furnished with this text. - In both cases, the sides of the cards must be parallel to the grid lines whe used. The cards are divided into tenths, and when read to the nearest graduation will give a reading to one decimal, or to a tolerance of 100 yards. When readings to two decimals, or to ten yards, are desired, the graduations are further sub- divided into tenths, by inspection. Plates 5 and 6 show the vertical edge of the grid coordinate card placed directly on the point whose coordinates are desired. In this case it is only necessary to place the card with its horizontal edge on the horizontal grid line and slide it out horizontally along the grid line until the vertical edge reaches the point whose coordinates are desired. The square coordinate card can be readily improvised by using any square piece of cardboard or heavy paper. * 14. Coordinates on the 5000-Yard Grid Maps. The smaller scale maps, such as the tactical map (1:62,500), often show every fifth grid line only, thus dividing the map into 5000-yard squares. This fact is quickly determined by noting that the numbers on the grid lines are in multiples of five. (See Plate 6). In indicating location by the “grid-square” method, it is sufficient to indicate the squares as they appear on the map. Thus the grid square in which P is located in Plate 6 is (40–85). To indicate exact location by the grid coordinate method, however, it is necessary to allow for the intermediate 1000-yard grids that are omitted from the map. For this purpose a special coordinate card is used, dividing the 5000-yard unit into five 1000-yard divisions for the missing intermediate grids, and further subdividing each of these 1000-yard units into tenths (or 100-yard units). Such a coordinate card and its method of em- ployment is shown in Plate 6. Practical Exercises (All exercises herein are based on Special Map “A” of this text.) 1. Give the location of each of the following by the “grid square” method: a. HOLLIDAY HILL (center of sheet). b. NALLE HILL (upper left of sheet). c. 52d INFANTRY WOODS (right of sheet). 2. Give the grid coordinates to the nearest 100 yards of the center of each of the following features: a. OLIVER HILL (20-18). b. 4th INFANTRY WOODS (17-18) c. BUMA HILL (23-20) LOCATION AND COORDINATES 15 3. Give the grid coordinates to the nearest 10 yards of the center of each of the following features: - a. Road junction (22-22). b. House on HOUSTON HILL (18-21). c. Stream junction (24-21). d. Northern house on SACKETT HILL (22-20). e. Point where the railroad crosses the highway north of the 58th IN- FANTRY WOODS (20-20). 4. What do you find at the following locations? a. (22.77-21.42). b. (1748-1783) c. (1879-1972). d. (20.94-1724). e. (23.75-2250). 5. Give the location of the following features by the polar coordinate method: a. Road junction (24.28–21.88). b. Hill (23.48-2003). c. Woods (22.00-2156). d. 30th INFANTRY WOODS (18-19). 6. The conventional sign used on Special Map “A” for “Bench Mark” is incorrect. What is a Bench Mark, and what is the correct conventional sign? 7. Each of the following coordinates contains one or more errors. What are the errors, and what are the correct coordinates? a. House 1421.54–1020.5. b. BM 415 (1873-20.70) (South of HAWKINSON HILL). c. BM 422 (1842-2030) (South of BOUTON HILL). Note: Solutions to these exercises will be found in the Appendix (Par. 85). Students are urged to prepare their own solutions before consulting the Appendix. CHAPTER III DISTANCE AND TIME 15. Scales. Maps are made to scale. This means that a certain distance on the map represents a fixed distance on the ground. For example, if one inch on the map represents one mile on the ground, the map has a scale of 1 inch = 1 mile. Included in the basic data on a map is a map scale which consists of one or more lines divided into equal divisions, each major division being marked with the distance which it represents on the ground. These are graphic scales ! O OO SOO O ! O OO 2 O OO 3 OOO 4. OOO |-I-TETET= | - º E. Yards HExtension + Primary Scale —- Plate 7. A Graphic Scale for Measurements in Yards. and are used for the measurement of distances. Usually, there will be one scale graduated into mile units and fractions of a mile for use in march and time distance computations and another graduated in yards for direct measure- ment of ranges, frontages, and depths. (Plate 7). Each scale consists of a primary scale, that part to the right of the zero, and an extension, that part to the left of the zero. The extension consists of one primary unit of the graphic º B distance sº- |- (strip of paper) 1 OOO O iOOO 2OOO 3OOO 4000 º distance —- Plate 8. Measuring a Distance on a Map. scale subdivided into appropriate fractions. The scale in Plate 7 has 1000-yard units for the primary scale and 100-yard units for the extension. * 16. Distance Measurements. Distance measurements on the map may be determined by use of the graphic scale. Since the graphic scale is printed on the 16 DISTANCE AND TIME 17 margin of the map, it cannot be used directly as a ruler to measure distances. To measure the distance between points A and B, take a strip of paper and lay its straight edge so that it passes through the two points on the map. Mark on the paper short straight marks (known as ticks), vertical to its edge and di- rectly opposite the two points. The distance between the two ticks on the paper is the map distance between the points. To determine the ground distance, move the marked paper to the proper graphic scale and place the right-hand tick accurately on that division of the primary scale which allows the other tick to fall within the extension. Then read the total number of the primary units to the right of the zero and add the number of graduations included on the extension. The combined reading will be the ground distance. The distance between points A and B (Plate 8) is 3000 yards of primary scale plus 4.2 divi- sions of the extension, a total of 3420 yards. If the distance is greater than the length of the graphic scale, apply the primary scale one or more times until the remainder can be measured as previously explained. If measuring the road distance between two points on a winding or irregular road, it is only necessary to break the route to be measured into a succession of approximately straight parts, commonly called legs. Following the method of Plate 8, use ticks to mark the legs on a strip of paper. The combined distance, so plotted, is then measured directly on the graphic scale. 17. The Representative Fraction. The scale of a military map is indicated on the map not only by the graphic scale but also by a fraction known as the “Representative Fraction” (abbreviated “R.F.”). This fraction expresses mathematically the relation which a distance on the map bears to the corre- sponding distance on the ground. Thus, for a map whose R.F. is 1/20,000, any distance measured on the map is one twenty-thousandth of the same distance on the ground; vice versa the distance on the ground is 20,000 times as great as it appears on the map. The map reader depends on the graphic scale for measuring distances; the map maker uses the R.F. The map reader should realize that a map with a R.F. of 1/5000 has a scale four times as large as one having a R.F. of 1/20,000. See the Appendix (Par. 77) for the R.F.'s of our standard maps. 18. The Map Measurer. The map measurer is an instrument specially designed for quickly measuring distances on a map. It consists of a dial case, handle, and a small wheel or roller. A moving pointer indicates on the dial the distance traveled by the wheel rolling along the line to be measured. Unless the map measurer is graduated to the particular scale of the map being used, it is necessary to convert the units shown on the dial of the instrument to the required units of ground distance. To measure distance with a map measurer proceed as follows: 18 MAP AND AERIAL PHOTO READING (1) Turn the small roller at the side of the dial case opposite the handle to set indicator of map measurer at Zero. (2) Set the roller at one of the given points and, holding the handle vertical, roll along the line to be measured to the second point. (3) Under the pointer, read the distance on the divisions on the dial corresponding to the R. F. of the map. ºr E. Plate 9. Map Measurer. (4) When there is no scale corresponding to the R. F. of the map, read the one marked 1:10,000 and multiply by the denominator of the R. F. divided by 10,000. - (5) Some dials are divided to read the map distance in inches or centi- In eterS. 19. Measuring Distance By Road. Road distance between two points, be- cause of the bends and turns of the road, seldom can be measured in one operation as explained above. It is necessary to break the route to be measured road distance (strip of paper) Plate 10. Measuring Road Distance. into a succession of straight parts, commonly called legs, plotting them in sequence direct from the map onto the edge of a strip of paper. (See Plate 10). The combined distance, so plotted, is then measured on the graphic scale (always in miles for marches and movement). DISTANCE AND TIME 19 20. Words and Figure Scales. Scales may also be expressed in words and figures, for example: “One inch equals one mile.” This means that one inch on the map represents one mile on the ground. Such a scale can be converted into a representative fraction by having both sides of the equation in the same unit of measure. The scale mentioned above would be “1 inch = 63,360 inches,” and its R.F. would be 1/63,360. 21. Conversion of Distance to March Time. It is often necessary to convert distances measured on a map into the time it will take for a movement by troops either on foot or in motors. The distance to be marched divided by the hourly rate of march gives the time required for the march. Foot troops habitually march on roads, by day, at an average rate of 2% miles per hour when allowance is made for customary rests. If the distance measured on the map is determined by the graphic scale to be 11.4 miles, the march time for foot elements by day would be 11.4 + 2.5 = 4.56 hrs. = 4 hrs. 33.6 mins. All fractional parts of a minute are carried to the next full minute, making the march time in this case 4 hours and 34 minutes. 22. Converting March Time to Distance. Frequently it will be necessary to determine the distance a column can march during a given period of time. The time in hours multiplied by the hourly rate of march will give the dis- tance. For example, a motor column averaging 25 miles per hour will cover 3 x 25 = 75 miles in three hours. To determine where the column will be at the end of the given time, the distance should be plotted on the edge of a strip of paper by means of the miles graphic scale and then scaled off along the legs of the road by marking the ticks for each leg along the measured portion of the strip of paper. Of course a map measurer could be used to run off the 75 miles, but the beginner should be very careful to do this accurately. Practical Exercises (All of these exercises are based on Special Map “A”.) 1. What is the straight distance, in yards, from BM 471 (19-20) to BM 423 (21-19) P 2. What is the straight distance, in yards, from the house (21.04-1994) to the house (23.91-18.10) P 3. What is the distance, by road, in miles, from BM 440 (18-21) to crossroads (22.57-17.68) via the MARNE and KEYSTONE ROADS? 4. How long would it take foot troops traveling at 2% miles per hour (mph) to march the distance in 3 above? 5. Assume, for the purpose of this problem, that the scale of this map is “one inch equals one mile.” The head of a column of foot troops two miles long . . 20 MAP AND AERIAL PHOTO READING marching east on the FIRST DIVISION ROAD at 2% mph passed road junc- tion (19.68-2055) at 8:47 A. M. They will halt at 11:30 A.M. for one hour for lunch. - a. Where will the head of the column be when it halts for lunch P b. At what time will the head of the column arrive at road junction (22.28- 20.95)P * c. At what time will the tail of the column clear this point? NOTE: Solutions to these exercises will be found in the Appendix (Par. 86), but the student is urged to endeavor to solve all the problems before referring to the solutions. CHAPTER IV DIRECTION AND AZIMUTH 23. General Direction. One of the most important operations in map reading is to determine the direction from one point to another. This applies to the map itself and to transferring these directions from the map to the ground. The established geographic terms north, south, east, west, and similar terms such as northeast, are used in the army to indicate general direction. The rela- tive terms right and left, front and rear, are also used in the field. These terms are used in their generally accepted sense, except that the relative terms de- pend upon the direction the unit is facing rather than the individual; in com- bat, the direction of the enemy is always front. When a more accurate desig- nation of direction is necessary, the azimuth method is used. 24. The Azimuth Circle. To measure anything there must be an origin or initial point and a unit of measure. In the case of direction, the origin is some known line passing horizontally through the point where we are standing or from which we wish to measure direction; the units with which we measure are either degrees or mils. In the azimuth method, the observer or the point from which the measurement is initiated is assumed to be at the center of an imaginary horizontal circle (Plate 11). The circle is divided into 360 equal units of angular measurement, called degrees. Each degree is divided into 60 minutes; each minute into 60 seconds. The degrees are numbered in a clockwise direction, the zero being at the north, which automatically places the 90-degree mark exactly east, the 180-degree mark south, and the 270-degree mark west. The 360-degree point coincides with the zero point (north). Azi- muths are always measured from the zero or north point clockwise around the circle. In military parlance a line which goes directly east has an azimuth of 90°. The mil is discussed in Paragraph 30. 25. The Protractor. Map azimuths are read with a protractor. Two standard types of protractors, semicircular and rectangular, are shown in Plate 12. Each protractor represents one-half of an azimuth circle. Two scales are usually shown, one reading from 0° to 180° for reading azimuths in the first or right half of the circle, and another showing readings from 180° to 360° for azimuths in the second or left half of the circle. 26. Measuring a Map Azimuth. To measure the azimuth of a line on a mili- tary map, extend the line to be measured, if necessary, until it crosses a vertical grid. (See Plate 13). Place the central index point of the protractor upon the intersection of the line with the vertical grid and register the base line of the 21 2OO 16O | 9 O 15o 170 SOUTH Plate 11. The Azimuth Circle. The azimuths of A, B, C, D, and E are 22°, 78°, 135°, 240°, and 313°, respectively. Ję 2O º &Q º W99 tº: tº Q zoo º O º º ©ºo * * .. §: Q *. º ſº * g3 º, sº Q & $º 3 & º 2 §3 3 ſº a 3 & tno * §3 <- #8 Nº me © E {Nº wºme © & tº & © Ap & - & S. 3? Gº = #: 33 & CŞ {º sº ©, º 38 & º, cº ovº • 636 oº est ort & o!" ©!! Q91 A B Plate 12. Map Reading Protractors. A—Semicircular Protractor. B–Rectangular Protractor. LINE EXTENDED TO CUT PROTRACTOR SCALE TO FACILITATE READING. 36O `s. EXTENDED TO INTER VERTICAL GRID. |8O SECT 18O Plate 13. Measuring Map Azimuths. The azimuth of the line A-B is 63°; of C–D, 2.98°. BASE LINE CONSTRUCTED **-īājī Hºstići. To O VERTICAL GRIDS., R | S6S | |NITIAL POINT | O FROM WHICH AN O AZIMUTH OF | | 15° IS TO *s, PLOT TED. 4s O P | Y ~ O | Y-- i>s AA-POINT_PLQTIED FROM & ºf ~ PROTRACTOR SCALE | 8 O N / Soº - LINE DRAWN FROM P THROUGH F.' sº * * | | smºs--- j | | Plate 14. Plotting an Azimuth (115°) On a Map. 24 MAP AND AERIAL PHOTO READING protractor accurately on the grid line. If the direction of the line to be measured is to the east of the grid line, the reading is taken from the 0° to 180° scale. If the direction of the line is to the west of the grid, the protractor is inverted, and the reading made on the 180° to 360° scale. Plate 15. Back-Azimuths. 27. Plotting an Azimuth on a Map. To plot an azimuth on a map, construct a vertical base (zero azimuth) line through the point at which the azimuth originates. On a gridded map such a line would be parallel to the vertical grid lines. Register the protractor with its base line superimposed on the plotted line, and with its central index on the point at which the azimuth originates. Mark the point opposite the proper reading on the protractor scale and draw the line as shown in Plate 14. 28. Back-Azimuth. Every line has two azimuths, depending on the direction in which the measurement is made. On Plate 15 the azimuth of the line O-A is 60°. The azimuth of the same line measured from A back toward O (A-O) is 240°. This is the back-azimuth of A-O. It is also the same as the azimuth of the line O-A", which is the extension of the line A-O. The back-azimuth of any line varies from its direct azimuth by exactly 180°. Therefore, whenever the azimuth or the back-azimuth of a line is known, its other azimuth can be determined by subtracting or adding 180°. If the direct azimuth is less than 180°, add 180° to obtain the back azimuth; if greater than 180°, subtract. It is essential in dealing with azimuths always to indicate the direction of the DIRECTION AND AZIMUTH 25 measurement (O-A or A-O) and to specify azimuth or back-azimuth. On Plate 15 the azimuth of the line O-B is 290°; its back-azimuth is 110°. 29. Intersection and Resection. We have seen that an unknown point can be located by determining its azimuth and measuring its distance from a known point. However, if the unknown point is in enemy territory or across a swamp or river, it may be impracticable to measure the distance. By means of intersection and resection, azimuths alone can be used to locate unknown points. No measurement of distance will be involved. a. Intersection. Assume that an enemy gun (Plate 16) has been spotted be- hind his lines in an open field away from any easily-described landmark. We wish to locate this position accurately on our map. Both RJ 516 and RJ 482 are in our territory. From RJ 516 the azimuth measured in the field to the gun is 30°; from RJ 482 the azimuth is 112°. Now draw these two azimuth 482 (ſee 2-º Plate 16. Intersection and Resection. The azimuths from the road junctions to the gun being known, their plotting gives the location of the gun. Or the azimuths from the gun to the road junctions being known, they can be converted to back-azimuths and plotted with the same result. 26 MAP AND AERIAL PHOTO READING lines on the map. Their intersection is the location of the gun. This method is known as intersection. Care should be taken to make the measurements from points so that the intersection will be at about a right angle, this in order to get a clear-cut intersection. b. Resection. Now reverse the situation. You are locating a gun as shown in Plate 16 with no landmark nearby from which to spot on the map the position of your gun. RJ 516 and RJ 482 in the enemy's territory are visible and both of these points are on your map. From the gun position in the field the azimuths to the two road junctions are measured, 210° and 292°, respectively. Convert these azimuths from the gun to the known positions to back-azimuths of 30° and 112°, respectively. Plot these on the map from the known points, RJ 516 and RJ482, and the gun position is accurately shown on the map. This method is known as resection. It is the same process as intersection except that the original readings are taken at the unknown point and must be converted to back-azimuths to plot them from the known points. 30. The Mil. Fire direction of artillery, machine guns, and other auxiliary weapons requires greater accuracy of direction than is possible with degree readings. For this purpose the military have devised an azimuth circle divided into 6400 units of measurement known as mils. (See Plate 17). Protractors and compasses are provided, graduated in mils so that readings can be made direct in mil units without necessity for conversion. The method of reading and plotting azimuths in mils is the same as when using degrees. A protractor graduated in mils is furnished with this text. As 360 degrees are equivalent to 6400 mils, we see that one degree equals 17.7+ mils; 100 mils equal 5.6°. 31. Declination. The north-south grid lines used on military maps are parallel to each other and point to grid north, which is slightly different from true north. Also, the magnetized needle of the compass (Par. 50), which is usually employed to measure directions in the field, points to magnetic north, which is different from either grid north or true north. The difference in di- rection between true north and either magnetic north or grid north is known as declimation. Therefore, there are two kinds of declinations, one known as magnetic declination (difference between true north direction and mag- netic north direction), the other as grid declination (difference between grid and true north). Note that both declinations are always measured from true north. Also note that magnetic north is indicated by an arrow, true north by a star, and grid north by the letter “y,” meaning the direction of the vertical or y grid line. a. Magnetic declimation. The magnetic declination in the United States varies from 25° east in the State of Washington to 22° west in Maine. It is obvious that allowance must be made for such large differences. More- DIRECTION AND AZIMUTH 27 NORTH WEST EAST 4OOO 24OO 3600 32OO 2800 SOUTH y Plate 17. The Mil Azimuth Circle. The azimuth of A is 2140 mils. 4-2 as e e ‘º e over, the magnetic declination at any given locality does not remain constant but has a small 6° 4O’ à CY annual change. ! É b. Grid declimation. Grid declination reaches a % 3 maximum of 3° either east or west of true north, + : depending on the locality. However, the grid I declination remains fixed for any given locality. In other words, for any given locality the direc- tions to grid north and to true north do not vary. c. Orientation symbol. Every standard map shows in diagrammatic form the relation of magnetic, grid, and true north; also the annual magnetic change and whether it is increasing or decreasing. Plate 18 shows a typical orientation symbol. This symbol gives the following basic APPROXIMATE data: wen otºion Magnetic declination: 6° 40' west (in 1935) ANNUAL MAGNETic CHANGE Grid declination: 2° 25' east (does not change) INCREASE 3°. Annual change in magnetic declination: 3' Plate 18. §:tºlentation (increase) M. and A. SIM. 28 MAP AND AERIAL PHOTO READING Plate 19 shows diagrammatically the relation between the three types of azi- muth. For practical map reading no attempt should be made to read or use azimuths closer than the half degree, as the compass is not accurate closer than one-half degree. For example, with the orientation symbol of Plate 18, we find the magnetic declination in 1941 would be: | ; TRUE AZIMUTH 2^O 2%renovate 2^ Mean oeclinarion / * 1935 / / 2^ ANNUAL MAGNETIC CHANGE / / / • INCREASE 3' / / ** / / / 2^ N N / / / * l" N N. N. 2^ / / A N. N. / N ^ *s * ,” Z ~ Y ~ e” ~ * * ~ - - - T ..º-ºp BACK AZIMUTH >~~~TTL--K TRUE BACK AZIMUTH MAGNETIC BACK AZIMUTH Plate 19. Relationship Between Azimuths. Magnetic declination (1935) 6° 40' (west) Change in 6 yrs.-5 x 3’ (Increase) 18' Magnetic declination (1941) 6° 58' (west) However, in the field use the nearest half degree; the above figure then be- comes 7°. If the declination had turned out to be 6° 20', you would use 6%", the nearest half degree. 32. The Grid-Magnetic Azimuth Adjustment. The three lines, grid north, true north, and magnetic north, may occur in any one of several arrangements. The amount and direction by which the grid north varies from the magnetic DIRECTION AND AZIMUTH 29 north is the correction data needed in map reading. The amount of this ad- justment may be the sum of the declinations, or in other cases may be the differ- ence of the declinations. Both the amount and the direction can be determined from the diagrammatic plotting of the orientation symbol and the values given thereon. First study the symbol and determine the mathematical amount of the variation between the grid and the magnetic north lines as shown. (See >k 3° *—| 4° 8° 6° abºver ADJUSTMENT | | * adjustypt Q GRID 2 y ſAZ! MUTH \? \\?--T Tºs / / --~ * •e ee N & / `.../ “... & y “a Z ׺ 2. / / MAGNETIC / AZIMUTH / GRIP AZ. = x. ... GRID Az. = x. ... GRID Az. = x . . . MAG. AZ. = X-F || MAG. AZ. = X - 5 MAG. AZ. = X* + 2* Plate 20. Determining the Grid-Magnetic Azimuth. (Angles exaggerated) Plate 20.) Then note whether the magnetic arrow lies inside (right) or outside (left) of a clockwise azimuth measurement from the grid line. If it lies inside a clockwise measurement, the magnetic azimuth will be less than the grid azimuth by the amount determined. If outside (left), it will be greater than the grid azimuth. Plate 20 shows a diagrammatic method of determining the grid-magnetic adjustment for three separate instances. 30 MAP AND AERIAL PHOTO READING Practical Exercises (These exercises are based on Special Map “A”.) 1. Measured from BM 415 (20-18), what is the grid azimuth of each of the following points? a. BM 423 (21-19). b. BM 300 (22-18). c. BM 383 (19-17). d. BM 471 (19-20). 2. What feature is found at a distance of 1820 yards and on a grid azimuth of 100 degrees from BM 423 (21-19) 3. Give the following data pertaining to this special Map “A.” a. The magnetic declination for 1940. - b. The grid declination. c. In order to convert a grid azimuth taken from this map to a magnetic azimuth, what is the amount and the direction of the adjustment for 1940? 4. A platoon commander, directed to attack from BM 302 (23-17) toward BM 374 (22-18), set his compass to insure correct direction in passing through the woods. What azimuth should he set on his compass? 5. For the purpose of this and the following problem, assume that the orien- tation data shown on the map is Magnetic declimation 5° west; Grid declimation 3° east. A patrol from a position at BM 471 (19-20) saw enemy digging en- trenchments in the distance. The patrol leader, with his compass, determined the azimuth to the enemy position to be 123°. The patrol proceeded east on the FIRST DIVISION ROAD. Arriving at BM 449 (21-21) the patrol leader climbed a tree and again saw the same enemy position and again determined the azimuth, which was 207°. What was the location of the enemy position? 6. A patrol in the field took the following compass readings: To BM 418 (18–19), 291° To BM 416 (18-17), 228%? º What was the location of the patrol at that time? CHAPTER V ORIENTATION 33. Definition. A map is oriented when, in a horizontal position, its north line actually points north. This results in all lines of the map automatically becoming parallel to the corresponding lines on the ground. The map reader is oriented when he knows his position both on the ground and on an Oriented map and the north, south, east, and west directions on the ground. It is of prime importance that the map reader thoroughly understands these two operations. as a * J dº Q- _-_z= gº Jºš–-foºzg º * %2, TTS – ~~ cº...?'.3: * \ §§ed.”. ... -->02, *—º —-if Plate 21. Orienting the Map by Inspection. 34. Methods of Map Orientation. a. By inspection. By carefully observing the road system and features in the immediate vicinity, the map may be oriented as follows: Lay the map in the road. Rotate the map horizontally until the road as shown on the map parallels the road on the ground, checking to see that the positions of the nearby ground features are in similar relation to their corresponding conventional signs on the map. The map is now approximately oriented. This simple method, as illustrated in Plate 21, is the most practical 31 32 MAP AND AERIAL PHOTO READING method for ordinary purposes. It may also be used as a rough check on more accurate methods. b. By compass. Magnetic north is shown on the map and is also indicated in the field by the north needle of the compass (Par. 50). To orient the map by means of a compass, follow this method. Ist POSITION MAGNETIC NORTH !MAP NOT ORIENTED Direction orrows on margin of map Composs- (JN) with north-south, axis ? of case coincident with line ob * MAGNETIC 2nd POSITION NORTH MAP ORIENTED —a MAP * =s=ºs Plate 22. Orienting the Map by Means of a Compass. (1) Prolong the magnetic north line on the map or draw a line parallel to it (as a-b in Plate 22). (2) Place the compass over this line with the north point of the compass ºsseduuoo Kq ºſťIN 9ų) ſuņuoſio ºgg94€IJI 34 MAP AND AERIAL PHOTO READING pointing toward the marked north-south axis of the compass. Rotate the map horizontally under the compass until the line a-b on the map coincides with the magnetic needle. The map is now oriented. (See Plate 23.) c. Without compass. In case a compass is not available and no suitable road is available for the method by inspection, the map can be oriented by a third method. (1) Select on the map two points which can be identified on the ground and are visible from each other. (Houses or water tanks or even well-defined hill tops are suitable.) (2) Through the two points on the map draw a long straight line. (3) Standing on the ground at one of the points, rotate the map horizon- tally until the line drawn on the map is on the same general line as the line connecting the two points on the ground. The map is now oriented. s\'ºs--- ass===== *=e * Plate 24. Orienting the Map by Ground Features. Plate 24 illustrates this method. The observer is too far from the road junction, and the road is too winding to use the method by inspection. How- ever, having spotted his position on the map, it is a simple matter to draw on the map the line to the farmhouse. This line is then used to orient the map. 35. Locating Your Position on the Map. a. By inspection. When an individ- ual knows his approximate location on the map, he studies the visible terrain for distinctive features, and the map to locate and identify these features. He estimates the distance and direction to the features on the ground and notes the corresponding distances and directions on the map. Location by inspection is greatly simplified if the map is oriented to the ground (Plate 25). b. By single point. To locate one's position on the map while traveling a known road, proceed as follows: Orient the map. Select some distant feature ORIENTATION 35 of the terrain that can be located and identified on the map. Place a pin through the feature on the map. Take a pencil or any straight edge, hold it against the *- :- Él Él É -ºs- Sº **s § * §§ sº 5& 3 *S **S Plate 25. Locating Position on the Map by Inspection. pin, and turn it until it points at the feature on the ground. Draw a line on the map along the edge from the pin toward the road. The point where this line intersects the road is the location of the position. Check the results by studying the near-by terrain features and comparing them with the map. N N w HOUSE N. - * Tºjº N - N Q. - MAP ORIENTED POSITION OF |BY COMPASS OBSERVER Plate 26, Locating Position on the Map by Resection. 36 MAP AND AERIAL PHOTO READING c. By resection. (See Paragraph 29.) To locate one's position on a map in the field by resection, proceed as follows: Orient the map accurately. Select a distant visible feature of the ground and locate and identify it on the map. Place a pin in the feature; place a pencil on any straight edge against the pin, and turn it until it points at the feature on the ground. Draw a ray on the map from the pin toward your position. Select a second feature, at as nearly . a right angle as possible from the first feature. Repeat the operation. The inter- section of the two lines is the desired map location. During the entire procedure the map must remain oriented. This method is of value when no well-defined landmark is near your position. 36. Distance. Often orientation includes measurement of distance. When time is available and the tactical situation permits. pacing or taping (chaining) may be done. However, these methods are more accurate than necessary in most instances of field service. Along highways when traveling in motor vehicles, advantage should always be taken of the odometer readings. For movements other than by motor, distances will normally be estimated by eye. CHAPTER VI ELEVATION AND RELIEF 37. Importance of Ground Forms. Thus far we have regarded the map as representing a flat surface and have considered only the horizontal positions of the features indicated thereon. We now come to the very important subject of elevation. From this we can determine the relief of the terrain—the hills, ridges, and valleys. A complete topographical map portrays these ground forms. The trained map reader visualizes them from the information shown on the map. Ground forms enter into practically every use of the map for military purposes. A knowledge of them is necessary to select defensive posi- tions, fields of fire, objectives in attack, and in the determination of visibility both for purposes of observation and for delivering fire. 38. Elevation. Elevation is the measure of vertical distance above a known datum plane. For standard maps the datum is zero elevation at mean sea level. Elevation is expressed in feet above mean sea level and is shown by con- tour lines on the map and by elevation numbers placed on prominent hills or mountain peaks and often at crossroads and road junctions. 39. Contours. Since the map is flat, a special conventional sign known as a contour is necessary to show elevation. A contour line represents an imaginary line on the ground every part of which is at the same elevation. In mapping, only the contours at regular intervals are shown. Contour lines show the shapes of the hills, mountains, and valleys as well as their elevations. Plate 27 shows the relation of the contour lines to the elevations on a hill. The student should note that the spacing of the contours in the plan (Figure 1) corresponds to the steepness of the slope in the profile (Figure 2). One walking along a contour line goes neither up nor down hill but always on the level. 40. Characteristics of Contours. The following are some basic characteristics of contours: a. They are spaced at uniform vertical intervals. b. A contour on the ground cannot begin or end. It eventually closes on itself. On a map a contour line may appear to end, but this is only because it runs off the sheet. This is illustrated by the shore line of a lake. A person following the shore line far enough must eventually return to the starting point. c. A contour cannot join or cross another contour. (An apparent exception exists in the rare case of vertical or overhanging cliffs.) d. A contour which, closes within the limits of a map indicates a summit or a depression such as a pond. (If there is no water in the depression, a special contour line known as a depression contour must be used to differentiate it from a summit.) 37 38 MAP AND AERIAL PHOTO READING e. All points on one contour line have the same elevation, and only points on the same or equal contour line can have that elevation. f. To “cross” a ridge, a contour must go around the outer end of the ridge. In doing so, it usually assumes a U trace or shape. iable Horizontal Distances are Va. ºl--- kºmm’sº * Toº" "S’ º §asured this wag & Lº * º † Vertical Intervals :* ..., A Nº. # %re fixe4 - || > || 49.2° +-f SNZ | 1; Wag 3O Aſº º j º I à | 2O aſſº } f N / 101. #. ſ } O Horizontal Plane (Datum) º h Fig. 2 - Profile Plate 27. Plan and Profile of a Hill. g. To “cross” a valley, a contour must go up the valley, cross the stream or drainage line, and then come back on the opposite side. It usually crosses the stream or drainage line with a V trace. The typical contour line is thus a curving line forming a series of V's for the valleys and U's for the ridges. ELEVATION AND RELIEF 39 A. The steeper the slope, the closer the contours; and conversely the gentler the slopes, the farther apart the contours. i. A contour always runs at right angles to the direction of the steepest slope. j. The steeper the slope, the closer the contours; and conversely, the gentler the slope, the farther apart the contours. k. Evenly-spaced contours indicate uniform slopes; irregularly-spaced con- tours occur on uneven slopes. The student should study both Plates 28 and 29 in order to learn the charac- teristics of contours as well as the terms given to ground forms. & cº-f *** sº †-2---eiðº sº ſº - 2 "._32.2° 22. ºùWSFs * *, 2.22:2°23°. §§º 㺠*e * §ſº * W * * Sº, S. .. :: ; ... Y Nºss - % wºmmiſſ jºll!" gº §§ ~ * s % º ſū 2 %| %lſº F. : 2-2. Plate 28. Contours of an Area. The top figure is a sketch of the ground. The bottom figure shows how this ground would be indicated on a contoured map. 41. Contour Interval. The vertical distance in feet between one contour and the next is the contour interval. This information is usually given in the margin of the map as, for example, V.I. = 10 ft. (V.I. means Vertical Interval.) Should this information be omitted, the contour interval can be ascertained from the 40 MAP AND AERIAL PHOTO READING map by noting how many contour lines there are between the numbered contour lines. It is customary to number every fifth contour. Often these lines are made heavier than the others. For maps of 1/20,000 and 1/62,500 scale, a contour interval of 20 feet has been prescribed; for 1/10,000 maps, 10 feet. (See Appendix.) RIDGE ~~ ~ SADDLE NOSE VALLEY SPUR DRAW Plate 29. Contours of Characteristic Ground Forms. V : 2O F.T. Plate 30. Determining Elevation from Contours. 42 MAP AND AERIAL PHOTO READING 42. Determining Elevation. a. Of a point on a contour. To determine the elevation of a point on a map that happens to fall on a contour, search along the contour line for its stated elevation. This will be the elevation of the point. On most maps every fifth contour is accentuated for convenience, and often only every fifth contour is numbered. In such cases, note the vertical interval shown on the map, the elevation of the nearest numbered contour, and the number of intervening contours, and compute the elevation of the required contour. The elevation of Point A on Plate 30 is 580 feet. b. Of a point on a slope between contours. To determine the elevation of a point on a slope between contours, first determine the elevation of the two contours between which the point lies. Then note the relative position of the point with respect to these two contours and along the line of the steepest slope, which is the line perpendicular to the contours. Interpolate the distance in terms of elevation. Point B on Plate 30 has an elevation of 594 feet. c. Of a point above the top contour. In the case of a point falling within the top contour of a hill or ridge, only an approximation is possible. The elevation of point C on Plate 30 must be greater than 600 and must be less than 620 feet. Since the top of the hill itself cannot be as great at 620 feet (or the 620 contour would appear), and the point “C” is obviously not at the top of the hill, its elevation would be roughly estimated as 605 feet. 43. Terrain Structure. Since all the water from heavy rains or snows can- not seep into the ground, much of it must run off. At one point a brook be- gins; as it flows downward, another joins it; soon several have united into a fair-sized creek which rushes along, carrying its burden of soil into the main stream which in turn carries its silt through the large rivers into the ocean. This process, continued for ages, has formed our relief or terrain structure. The more resistant portions have remained as hills and ridges, the less re- sistant as valleys and stream courses. Therefore, the drainage net, as shown on the map, is the pattern of the low ground of the area. Between any two adjacent streams there will always be found a ridge or crest, its direction generally bisecting the angle between the streams and usually centrally lo- cated. The tops of the ridges are generally irregular, the high points constitut- ing hills or peaks which appear on maps as a succession of closed contours. The basic terrain structure consists of a drainage system, following a charac- teristic pattern, and a ridge system which conforms to and complements the drainage system. The best way to study the terrain structure of an area is to trace out the drainage system and then the ridge system. (Plate 31.) The exact location and trace of the drainage system is shown on maps by the proper conventional signs for streams. The exact location and trace of the ridge sys- tem can be determined by tracing along the lines established by the hills and ELEVATION AND RELIEF 43 ridges as shown by the contours. On a map it is preferable to use a blue pencil to accentuate the drainage system and brown or black pencils to mark in the ridge lines. Between every set of drainage lines there must be a ridge line. 44. Profiles. The simplest method of showing the slope of the ground is by making a profile. A profile is a cross section of a specific slope or hill cut by an imaginary vertical plane. g s * e” t €. E d g e of p O p ©r ſè ". * | F-T-T-I-I TT- I-I-I | | | | | | | | | | | | | 4 O H–H–H–H–H t d | | | | | | | | | | | | 3O H–H N | | | | | | | | | | | 2 O HK–H–H \ iſN | | | | | O H H N iſ 'N | || | OO k+2, k} 90 Figure 2. Plate 32. Construction of a Profile. a. To draw a profile between the points A and B on Figure 1 of Plate 32: (1) Connect the points by a straight line A-B and assume a vertical plane passed through this line. (2) Take a piece of cross-section paper or any paper on which horizontal, parallel lines have been equally spaced; cut or fold the paper along one of these lines. (3) Now refer to Figure 1 and determine from the contours the highest and lowest elevations along line A-B. The highest is 130, the lowest about 95. Number the lines on the paper consecutively, using 90 for the lowest and 140 for the highest. (Figure 2, Plate 32.) 44 MAP AND AERIAL PHOTO READING (4) Place the top edge of the paper along the line A-B on the map; bring point A down perpendicularly to a at elevation 130 and point B to b at eleva- tion 100. Where the edge cuts each contour line, drop a perpendicular to the horizontal line on the paper corresponding to the elevation of the contour line. (5) Connect the adjacent intersection points by a straight line. This broken line represents the profile. N- of paper WJW A | 4 O C. 2Line of sight, A to mosk C / 21 ź Ø º efilode NJ | 3 O S- Ns SS-à TS ; s 2% sº h | 2 O | | O \ & * * * * * < Height of mask 2 dC above line, of sight, Y4% A º 9 O Plate 33. Visibility by the Profile Method. | OO Line g sight, A to B | | (6) Especial care must be taken in determining the elevation of the crests and of the depressions along the profile. Where the line crosses a crest or de- pression, an elevation number on the map is often found to assist in determin- ing the exact elevation. Otherwise it must be interpolated from the spacing of the contours. For example, just to the left of B in Figure 2, Plate 32, the C. O ="Tº WU W. W W B º Militaru Topographical 2. Defilade Crest, Crest, *N D % Plate 34. Defilade. profile line crosses a depression, a stream course. Looking at Figure 1, we see that the point where the line crosses the stream course is about half way between the 90-foot and 100-foot contours (always measure along the stream course in a similar case). The elevation at the intersection is therefore estimated to be 95 feet and is so plotted on the profile. b. Vertical scale of profile. The horizontal scale of the profile is the same ELEVATION AND RELIEF * 45 as that of the map. However, the vertical scale should be greatly exaggerated. Figure 2, Plate 32 shows a suitable example. 45. Defilade. In Plate 34, O is the topographical crest, the highest crest of the hill; C is the military crest, the highest point from which the entire lower part of the hill can be seen. The observer at O is not able to see the ground at A due to the intervening mask at C. The ground at A is said to be “sight de- filaded.” The intervening defilade is called the “mask.” The amount by which the foreground at A is defiladed is equal to the vertical distance A-B. Plate 35. Visibility by Hasty Profile. 46. Visibility. Knowledge of the area which is visible from a given point or position or of lack of such visibility is very essential. The extent of the area visible affects the location of observation posts, the siting of weapons, the selec- 46 MAP AND AERIAL PHOTO READING tion of targets, avenues of attack, and the suitability of defensive positions. An area which is not visible from a given position is known as a defiladed area or dead space. There are several methods of determining visibility. Every officer and noncommissioned officer should be able to solve problems by these methods. a. By profile. This is the most accurate means. Plate 33 covers the same contoured area as Plate 32. It is desired to determine whether or not B is visible from A. Construct the profile as in Figure 2, Plate 32. Draw the line a-c (Plate 33) which is the line of sight from A tangent to the crest C on the map. This line strikes the ground at h. Therefore, that portion of the ground from H on the map to C is not visible from A. On the profile this is represented by the shaded area c-b-h. Point B falls in this area and is therefore NOT visible from A. If the observer at A had been standing, the line of sight would start from a point five feet higher (the height of his eyes) than the plotted position of a but would still be drawn tangent at c. º 3.2% ſº *% fºſ/ º Ü §ººk 6. yº Yº y y 2\º | Plate 36. Visibility of Areas. b. By hasty profile. Many problems of visibility can be solved without draw- ing a complete profile. In such cases, only the critical points which may affect the visibility need be plotted, these points being first determined by inspection of the contours. Such points would be the elevation of the observer, the probable masks (ridges), and the point whose visibility is to be determined. This is illustrated in Plate 35. It is desired to check the visibility of point B from O. By inspection the critical points are O, N, M, and B. Only the elevations of ELEVATION AND RELIFF 47 these critical points are plotted on the profile. Drawing the line of sight O-M shows that B (elevation 290) is not visible from O, due to the mask at M. On the other hand, point A is above the line of sight O-N prolonged and is there- fore visible from O. Similarly, point P (elevation 350) is visible from either O or M. Often visibility problems can be solved simply by inspection. For example, inspection of the map discloses that A is visible from N and B from M. c. By computation. This method can be used by those who understand the use of similar triangles. However, in view of the simple graphical methods outlined in a and b, it is not recommended for those not already proficient in the use of similar triangles. Method a or b will solve all problems normally encountered. d. Visibility of areas. By using the method outlined in a and running several profile lines from the observer's position through the area in question, it is possible to outline on the map the portion of the area which is visible by the observer and the portion which is not visible. (See Plate 36.) Practical Exercises (All exercises are based on Special Map “A”.) 1. What is the elevation of: a. The house at (18.71-19.68) * b. The church at (1751-17.43) P c. The stream junction at (21.28-1958) * d. The top of DAVIDSON HILL (19-19) 2. What is the location and the elevation of: a. The highest point on this Special Map “A” ” b. The lowest point on this Special Map “A”? 3. Identify the topographic features found at the following locations. Use the topographic terms: ridge, valley, spur, draw, hill or saddle. (See Plate 37.) a. (1977-1947). b. (21.64-1944). (22,08-2006). . (23.48-2003). . (23.33-20.27). f. (24.25-1906). . (23.30-1894). . (20.12-1874). 4. A detachment is traveling from DAVIDSON HILL (19.19) to RJ (2257. 1769) via the OHIO and KEYSTONE ROADS. Give the location to the nearest 10 yards and the elevation of the following: (NOTE–Disregard minor relief features of less than one full contour interval.) a. Each ridge line crossed en route. i 6. ; 48 MAP AND AERIAL PHOTO READING b. Each drainage line crossed en route. c. Give the location of the steepest up-grade encountered. d. Give the location of the steepest down-grade encountered. 5. An observer is standing on the top of ELLIOT HILL (18-18), elevation 442, looking northeast toward CR (20.37-1923), elevation 383. His eyes are 5 feet above the ground. a. Disregarding vegetation, can the observer see the CR (20.37-1923) b. What is the maximum elevation of a mask at the spur at (1962-1877) that would still permit observation of the crossroad? c. If the woods shown on the mask have a height of 30 feet, how much would this affect the visibility of the crossroads? d. What is the amount of defilade (vertical distance in feet of the target below the line of sight) at the stream at (20.14–19.08) P Disregard vegetation and use the spur at (1962-1877), elevation 402 feet, as the mask. 6. Construct a profile of the line from ELLIOT HILL (18-18) to CR (20.37-1923). & a. Verify by the profile the results obtained in 5 above. b. Indicate, by hatching, all of the ground along the line that is not visible to the observer on ELLIOT HILL. * c. Indicate the highest point (military crest) on the eastern slope of ELLIOT HILL from which riflemen in the prone position can see all the ground between them and the nearest stream. CHAPTER VII MAP READING IN THE FIELD 47. General. The map and the aerial photograph are the only means avail- able for studying distant or inaccessible terrain except by aerial reconnaissance. Even when the terrain is accessible, the map is still most valuable as a source of names and a convenient means by which to find one's way about. The officer should always take his map with him into the field and refer to it constantly. When operating over unfamiliar territory he should keep his movements plotted on his map, verify his location at every opportunity, and from his map learn the names of the terrain features encountered. 48. Terrain Feature Terms. The standard terrain terms, such as hill, ridge, stream, crest, and the like, are used in map work and in the field. For use in the field to identify more readily the special and the minor terrain features, a large number of less common terms are used. Those most frequently encountered are shown in Plate 37. 4 49. Distance. The determination of distance in the field presents many diffi- culties. Distance can be measured by pacing or by tape, but this method is slow, tedious, and often impracticable. Long road distances can be measured by the odometer of an automobile. Visible areas can be measured by estimation by eye. This requires a certain amount of skill and experience and is not successful in the dark, in woods, over long distances, or in broken country. Two other methods of handling distance in the field are the landmark method and the travel-time method. For example, a patrol is directed to proceed two miles down a road and take up a position in observation. The patrol leader could take a map, scale off two miles, study the map, and select some recog- nizable feature in that vicinity. He would then march until he reached the feature. On the other hand, if no map were available, he might calculate that the two miles would require forty minutes of marching. He would march forty minutes and then take position. 50. The Compass. Direction in the field is measured with the compass. There are four types of hand compasses issued in the service: prismatic, lensatic, watch, and marching. Plate 38 shows the prismatic and lensatic types. They are similar in design, construction, and employment. Each compass consists of a case containing a magnetic dial balanced on a jeweled pivot, a hinged cover with a glass window, an eyepiece containing a prism or lens for reading the finer graduations of the dial, and a holding ring. The glass cover has an etched line which is used like a front sight, and the eyepiece has a slot which can be used as a rear sight. The dial is fixed to a magnetized needle, rotates with 49 cLEARING peak - 5MALL 19A66 TOPOGRAPHICAL, 6KYLINE 5ADDLE 6TEEP { NO6E VALLEY O C1R1EST’ 5LOPE | CONVEX. OR. OR. Grą12 KNOLL ; 5LOPE SPUR. 1)RAW 18 OA1D TMILITARY f “glºgº CENTER. C1REST 13LUFF Nº E5A f VALLEY i Ny % //// / % º,--" 2- ~~ 2- * 2: . % w * - * 27%. 35.2 - * •+- * <- ~~< …" <_* ºr r- ~ * * * gº sº- Cº. 2. * sºrtà $36) j -ee" gº 4e / 7 / % % | //n} vº, T-2. -- 2’ | '''''''', *=-& ,” º | \, iſ/ !", ", \\li | . . . .s | % */º | * [. & vº ": §§ }|| 'ſſ; li'i' £ // sº-2 & {} • * > *** * % | %/ “sº se” Evereºf;:Né º/ // Sº…- # / % // S㺠• *Ča. tº Sº- t ºl, /// ſ/ * *===3.2% • ** Šºš. § <>? - ~ 2: . | | | / A Æ /, T2-3– := . * !!NS * sº ||| || 1 || 1 , , , , ...s:…”. &: Ǻ 2. 'I''' || | | 2. º. - *** T. sº gº =2'S 3. 24 *Aſ Jº, Jºº, 3–C. "Tº Lºs T DI pºz FºctricN ,J\ 2. %23: *~eº £32-,2sº Šs: S. Z/ as *… s *- NH3. S. %22% tº 4 Š cºosé1-OAD6 *s-s:= 22: **** Sºs * * aree ºf &º e” Ś. Of YTLOW TºAVE.1) ROAT) Lº g ~~ 7.3% **-sº Sºrrºs *::2-4 > *- ‘. .** ==== <== É& Ž%is/ºs TGs S Road - CULVETRT ſº/S/ºS ~ Sº JUNCTION * - *~. Sº Plate 37. Military Terms for Terrain Features. MAP READING IN THE FIELD 51 i The Prismatic Compass The Lensatio Compass LEGEND. A. Cover. . Front sight. B. Front sight. Index mark on case. C. Index markings on case. Movable index on crystal (luminous). D. Holding ring. . Rear sight. E. Lens. Prism mounting. F. Level. Clamp for compass card. G. Compass card or dial. . Holding ring. H. Xylonite indicator. Plate 38. Types of Military Compasses. H | D (T. % 32 ~22\,.\ |} sº → 2- 2 2 . © ſt |\º ×2 2" º F B A E. C A. Case. E. Front Sight. B. Compass card or dial. F. Holding ring. C. Cover. H. Movable index on crystal D. Rear sight (luminous) I. Dial needle. Plate 39. The Prismatic Compass Open. 52 MAP AND AERIAL PHOTO READING the needle, and is graduated for a full azimuth circle. Compasses are pro- vided graduated in degrees, in mils, and in both. There is an index mark inside the body of the compass near the hinge at which point azimuth readings of the dial are made. The cover can be used upright for taking field azimuths or opened flat for use on the map. The dial is locked by closing the cover and must be unlocked manually after the cover is opened. The line passing through the slot in the eyepiece, the center of the dial, the index mark, and the hair line of the cover is known as the axis of the compass. The compass needle is affected by the presence of iron, steel, or electricity, and will not give accurate readings near an automobile, tank, field piece, machine gun, or power line. A steel helmet, rifle, or pistol on the person of the observer may influence the needle and make readings inaccurate. E. : - - º - - º º Plate 40. The Marching Compass. Plate 40 shows the marching compass. It functions in much the same way as the prismatic type. The hinged eyepiece is a narrow piece of metal con- taining a magnifying lens in the larger circular opening. When the eye- piece is tilted so that it is aimed at the forward part of the compass face, the ob- server is able to see both the scale and a distant point at the same time. The outer scale is graduated in mils, the inner in degrees. The watch compass is being replaced by the marching compass. 51. Measuring Azimuth with the Compass. To read the azimuth of a point on the terrain (distant hill, house, etc.) proceed as follows: Raise the cover and the eyepiece and unlock the dial. Hold the compass to the eye and sight the compass at the object. Hold the compass steady until the dial comes to rest. Read the azimuth figure on the dial at the index point. This will be the magnetic azimuth of the line from the observer to the object. See Plate 41. To establish a given azimuth on the ground, proceed as follows: Raise the cover and lens and unlock the dial. Permit the dial to come to rest. Hold the MAP READING IN THE FIELD 53 compass to the eye and watch the dial, facing the entire body about until the desired azimuth figure on the dial is at the index point. Holding the compass in this position, look through the sights of the compass and pick up some ground feature on the line of sight. The line determined by this feature will be the azimuth desired. Do not wear Steel <1 is h – º helmet while read- /~ ing COmpa SS. } *…*- ſº º------> - Sã pº º:/. - - - -ams- Plate 41. Using the Prismatic Compass in the Field. 52. Marching by Compass. a. By day. Orders to troops may direct them to march or attack cross-country in a prescribed direction given in terms of azi- muth. Groups or individuals selecting cross-country routes from the map may compute the azimuth of various legs of the trip to prevent the possibility of LUMINOUS MARK SET BY THE NIGHT MARCHING SCALE. COMPASS SO HELD THAT LUMINOUS ARROW ON DIAL POINTS TO LUMINOUS MARK. lº Stºj Xºrº S 42. Compass Set for Night Marching. Plate getting lost. In any such case, map azimuths must be converted to magnetic azimuths before they can be used with the compass. To march by compass, the commander rotates the compass until the dial reads the required azimuth. 54 MAP AND AERIAL PHOTO READING He then sights along the axis of the compass and selects some hill, house, tree, or other feature on this line. He then marches toward the above feature until he reaches it, or it becomes invisible. He then repeats the operation, selecting a new feature on the line of the required azimuth upon which to guide the march. This is continued until the goal is reached (the compass is not in use while actually marching). The compass is used to select successive features on the required line, and the actual marching is always conducted toward such visible feature. The more distant and prominent the feature, the easier the procedure. b. By might. For use in marching at night, the compass is equipped with a movable luminous marker on the top of the case and with a night-marching azimuth scale on the outside of the case near the base. To set the compass for night marching on a predetermined azimuth, rotate the ring on the top of the case until the luminous mark is at the proper azimuth on the night- marching scale. Hold the compass in the hand with the dial free and turn the entire body until the luminous arrow of the dial points to the luminous marker. The direction of march is now the line of the axis of the compass. Select some feature such as a low star, skyline hilltop or saddle, or other recog- nizable feature on this line, and march in the direction of the feature selected. Repeat the operation as often as necessary and make frequent checks of the direc- tion while en route. The setting of the night-marching mark on its correct azimuth must be done before going into the field or by flashlight screened from enemy ground and aerial observation by an overcoat, shelter-half or other means. CHAPTER VIII READING AERIAL PHOTOGRAPHS 53. Introduction. An aerial photograph is a picture taken from any kind of aircraft from either a vertical or oblique viewpoint. Except for colors the ordinary aerial photograph conveys almost the same impression in image as received by the human eye from the same viewpoint. (Natural color aerial photography is being developed but is not yet in use). The images on the photograph at first appear strange, but this is because the person is not ac- customed to the viewpoint from the air. Aerial photographs were first used extensively during the World War. Since that time great progress has been made in equipment and in technique. The aerial photograph is here to stay, and all officers and noncommissioned officers should be familiar with them and learn how to use them. g 54. Uses of the Aerial Photograph. a. Intelligence. During a campaign the enemy positions and rear areas are photographed and the photographs carefully studied for indications of his organization, and for possible artillery and bombing targets such as supply points, assembly areas, command posts, and artillery positions. These features may sometimes be recognized directly from the photograph through their appearance. More often their appearance is carefully disguised, and their presence and identity must be deduced from . miscellaneous indications such as converging paths, regularity of Outline or arrangement, grass worn away or trampled down, muzzle-blast marks, and other similar clues. Important enemy areas are rephotographed from day to day and the latest photograph compared with earlier ones. Trees, bushes, and other detail on today's photograph that may appear entirely natural, may not appear at all on previous photographs of the same area, thereby disclosing their artificial nature. The comparative study of roads may show indications of abnormal traffic during the night, thus giving warning of the location of impending attacks or withdrawals. The study of the aerial photograph for the purpose of deducing enemy information is known as interpretation. It is a highly-specialized subject requiring special experience and training and is not the primary interest of the combat officer. b. Map making. The aerial photograph is very valuable as a basis for the construction of maps. Ground surveying for map making purposes is slow and laborious and is never possible in the case of territory that lies in the hands of enemy forces. The aerial camera records such features of the terrain as roads, railroads, towns, houses, streams, woods, and cultivated areas, and shows them in their proper size, shape, and relation to each other. From e: 55 56 MAP AND AERIAL PHOTO READING rectified photographs these features may be traced and maps constructed. Machines have been developed (the “multiplex” and the “aerocartograph”) which work on the stereoscopic principle (see Paragraphs 70-71) and by which contours may be plotted directly from overlapping aerial photographs. This use of the aerial photograph is technical and need not concern the combat officer. c. Tactical. Any commander needs detailed and reliable information con- cerning the terrain over which he must fight. Formerly, this information could only be obtained through personal reconnaissance and from maps. The aerial photograph gives an additional source of information regarding the terrain. Its great value in this respect is obvious in situations where personal reconnaissance is impracticable and when maps are not available. Even when maps are available, it is probable that there will have been many changes since their compilation. Old roads are often abandoned or resited, and new roads constructed, woods are cut down, and fields formerly cultivated are found grown up into brush and woods. Maps show these features as they existed at the time the data was compiled, which may have been years before. An aerial photograph, however, shows the terrain exactly as it is. The photograph is, therefore, a very valuable source of information with reference to the terrain, in that it gives reliable, up-to-the-minute information. It is in this connection that the aerial photograph is of great importance to the tactical officer. 55. Importance of the Aerial Photograph. a. The aerial photograph is a valuable instrument for conveying topographic information for the following TC2SOIlS. (1) It possesses in pictorial form a wealth of detail which no map can equal. (2) It is up-to-date. (3) It can be prepared for use in a short time, much quicker than making a new map. (4) It can be reproduced in quantity. (5) It can be made of an area inaccessible to mapping parties. b. It is inferior to a map in the following respects: (1) Important military features which can be emphasized on a map may be obscured or hidden on the photograph. .(2) Exact position cannot be given, thus preventing accurate measurement of distance or direction. (3) Elevations cannot be shown although a fair idea can be obtained of the ridges and valleys. t (4) It is difficult to read in poor light. Because of these limitations the aerial photograph does not constitute an ideal map in itself. The ideal situa- tion is to have both an accurate topographical map and recent aerial photo- ** ** AERIAL PHOTOGRAPHS 57 graphs. Plates I, II, and III* are reproductions of vertical photographs. The area which each covers is indicated on the corresponding topographic map (See map preceding the photo plates). The finished size of the standard single- lens individual print is seven by nine inches. To fit the page size of this book, the photo plates reproduced here are somewhat smaller than the original prints. |- Area covered assº" Shape of area covered by oblique photograph. (Broken Line) ~ Oblique photograph +. assº" * | i * = *sº H Plate 43. Scale Relation of the Area. Covered by an Oblique Photograph to the f Photograph Itself. 56. Types of Aerial Photographs. An aerial photograph is a perspective picture, with either a vertical or an oblique viewpoint, taken from aircraft. Except for colors and certain differences in relief, it conveys the same impres- sion in image as received by the human eye from the same viewpoint. a. Verticals. A vertical is the photograph obtained by pointing a single- lens camera at exposure so that the optical axis is perpendicular to the surface of the earth. (See Plates I-IV at the end of this section.) (Note. Plates referred to in Roman numerals, numbered serially from I to XII, are photographic plates and are to be found in this section. They should not be confused with plates with Arabic numbers). Since the camera film is horizontal, features on the ground are registered on a vertical photograph in perspective with little or no distortion in their relative shapes and sizes. The vertical is the most useful type for general military purposes and is commonly referred to as an aerial photograph. •Plates numbered in Roman numerals Will be found at the end of this chapter. 58 MAP AND AERIAL PHOTO READING b. Obliques. An oblique is obtained by intentionally tilting the optical axis of the camera. (See Plates V and VI). For best results obliques are usually taken with the optical axis of the camera inclined about 30 degrees to the horizontal and at comparatively low altitudes. The oblique photograph is a rectangle, but the area of ground covered by the photograph is a trapezoid. Plate 43 shows this relation. Obliques cannot be accurately scaled but are use- ful in emphasizing ground forms and in studying the vertical dimensions -ºil– -sº 32.3" - wº- "D" PRINT ! -—5.4° 2’ ** a tº * -- * * * ~ * A” PRINT —y"B" PRINT St H. C” PRINT | MO ~~ CAMERA NO. JOB LETTER AND ſh- k- SERIAL NO. OF PHOTO \ l wº & Collimating Notches E" PRINT + sº / iT 4– O Ç .9 * O Q9 .E. ſº Plate 44. Diagram of Composite Photograph Made with Air Corps Five-lens T-3A Type Camera. of terrain features. The oblique is an improved, economical, and quick sub- stitute for the panoramic sketch. A high oblique shows the horizon. On a low oblique all of the picture is below the horizon. c. Composites. A composite photograph is made by joining several photo- graphs taken simultaneously at a single camera position and transforming AERIAL PHOTOGRAPHS 59 them to a common plane. A multi-lens camera is usually employed in taking composites. (See Plate 44.) d. Mosaic. A mosaic is formed by joining several overlapping vertical photo- graphs taken at different camera positions. When the several overlapping photographs are oriented solely by matching the detail along the borders, the result is an uncontrolled mosaic. A certain amount of error occurs in this type of mosaic, and this error is exaggerated toward the Outer edges. When the several photographs are brought to a uniform scale, oriented and fitted to previously determined ground control points, the result is a controlled mosaic. When time, photographic rectifying equipment, and adequate ground control permit, the horizontal accuracy of a mosaic can be made to equal or exceed that of a standard large scale terrain map. In covering areas of con- siderable ground relief, this process requires ratioing each photograph in a number of sections, to reduce inherent relief errors of individual photographs. Normally, single prints making up the mosaic will be reduced to a common average scale, and errors of horizontal position caused by the variation of ground elevation will remain. Lithographic reproductions of controlled mosaics may be issued as special maps of territory not adequately mapped. Marginal information as to scales and azimuths, military grids, and a limited amount of descriptive matter are usually added prior to reproduction. If the mosaic follows along a single line such as a road or stream, it is called a strip mosaic. e. Pin points. If details of an isolated object or spot are particularly desired, a single photograph is taken with the desired object as near the center of the film as possible. This type of vertical photograph is known as a pin point. f. Photo-maps. If a single vertical photograph is reproduced by lithography with a graphical scale, a magnetic north line, and a local grid system, it is known as a photo-map. Scaled distances are only approximate. Contours are not usually incorporated in a photo-map. 57. Description of Photo Plates. The photo plates at the end of this chapter have been especially selected for their instructional value. The reproduction is superior to that usually encountered; but, as is always the case in lithographic reproduction, there is some loss of clarity over the original contact prints. Plates I, II, and III are of the same area but from different altitudes. These plates should be studied with care and in conjunction with the plottings on the map preceding the photo plates. A conception of the amount of area and the amount of detail to be expected from different altitudes is essential to any commander who may be in a position to order or to request photographic mis- sions. The only way that one can secure this conception is by a careful study of such photographs and their comparison in the matter of detail and in area. M. and A. SIM. 60 MAP AND AERIAL PHOTO READING Plate IV is an excellent terrain photograph and has the incidental value of containing certain military detail, such as a trench system, an artillery position, and parked motor transportation. There is also some transportation at the main artillery position. Moreover, a careful study of the photograph will dis- close other artillery firing positions, though less prominently. It contains excel- lent shadow relief. Plate IV overlaps slightly with Plate I, and more than half of it lies within the area covered by the map referred to in the previous paragraph. Plates V and VI are typical obliques at 3000 and 5000 feet, respectively, demonstrating the effect of elevation upon obliques. Incidentally, these photo- graphs cover much of the area contained in Plates I, II, III, and IV, and from opposite directions. Plate VII, top, shows a small stream, directly visible and easily recognized. The sand bars by their location behind the bends indicate that the stream is flowing from left to right. The highway bridge is concrete with two central pier supports. The center picture shows an artificial lake, the white border at the top being the dam. The vegetation in this small photo shows great variety, including everything from dense woods to barren, scrub-dotted slopes. The bottom picture shows typical cultivated fields and a cloud shadow. Inciden- tally, this is one of the highest pictures ever taken from a plane, having been taken at an altitude of over six miles with a temperature of about 62 degrees below zero, Fahrenheit. Nevertheless, the detail is clear. Plate VIII shows a typical village and contains various types of roads, a rail- road, cultivated fields, typical drainage, and very excellent terracing. Plate IX shows the outskirts of a city with converging highways of different types and a railroad. It also shows various types of minor drainage, terracing, cultivation, and vegetation. Plate X was selected because it shows clearly a typical drainage system. Plate XI is an especially fine print of minor drainage of different types, in- cluding artificial drainage ditches. Plate XII is a stereoscopic pair or stereogram arranged for use with the un- aided eye. Place a card vertically on the division line so that each eye can see its respective print only. Relax the eyes and the stereoscopic effect will develop. 58. Data on Aerial Photographs. When the aerial photographs are made up as a map, much of the data listed in Paragraph 75 may be found in its margin. More often there will be furnished single photographs on which will appear only the following legend: a. Index number to identify the picture and for filing purposes. b. Designation of squadron which took the photograph. c. Date and hour of flight. AERIAL PHOTOGRAPHS 61 d. Type and focal length of camera. e. General locality. (Often expressed in the map coordinates of the topo- graphic map of the area.) For example, the following is a typical legend: (V-43-74OC-16 OBSN) (12-21-41-9:32A) (12-15000) The V of the legend as shown above indicates that the photograph is a vertical; its serial number is No. 43; and it was taken of area 74OC by the 16th Observa- tion Squadron. The legend also indicates that the picture was taken on the 21st of December, 1941, at 9:32 in the morning, and that it was taken with a camera having a 12-inch focal length lens from an altitude of 15,000 feet. The name of the most important terrain feature, or the map coordinates of the center of the photograph are often added when known. In the case of a series of photographs taken for mosaic purposes this legend may appear on the first and last print of the series, the others showing their serial numbers only. Some photographs include an arrow %" in length in the lower left-hand corner indicating north, the letter N being superimposed over the center of the shaft of the arrow. 59. Orientation. a. By map. Maps are constructed with the north of the map at the top. All the lettering, grids, and figures are entered on this basis. However, aerial photographs are not necessarily taken on a north-south axis; often flying or tactical considerations prevent this. Moreover, the original prints frequently do not show any lettering or direction arrows for orientation. Therefore, it may be necessary to study the photograph from all angles to identify features to use in orienting it. Once features shown on the map are found on the photo, it is a simple matter to Orient the photo with respect to the map. A magnetic north arrow should then be drawn on the photo parallel to that on the map. On the photo there is no need to show either true north or grid north. Magnetic north will suffice for all measurements of direction. b. By shadow. Ground shadows recorded on aerial photographs are of tremendous importance in their effect upon the manner in which the mind of the reader interprets appearance.-Plate III has especially fine shadow values that cause the relief of the area to stand out clearly. The finger-type drainage lines in the lower center, with their pronounced valleys and separating dome- shaped spurs, are very apparent, as are also the two clear-cut gully-type drainage lines at the left of the photograph. Face toward the light and invert this photo- graph so that you are looking at it upside down. From this position the relief will appear to have reversed, the former valleys now appearing as encircling ridges, and the former spur ridge now appearing as an amphitheatre. The gully-type drainage lines, now on the right, will appear extruded, and even the woods will have an unnatural, pockmarked, crater-like appearance. Noth- 62 MAP AND AERIAL PHOTO, READING ing has changed in the photograph itself. If there is any change, it is in the mind of the reader. It is a form of optical illusion. Nevertheless, it exists and must be given full consideration. For this reason it is necessary that a photo- graph be correctly oriented for light when it is being studied for the recogni- tion of minor detail, especially relief detail. It is correctly oriented when the shadows on the photograph fall toward the reader. It is best to face toward the source of the light so that the light falling on the face of the photograph coincides with the direction of light as it fell on the ground. The direction of light can be determined from the shadows of buildings, lone trees, or the edges of woods. All the photographs in this text have been oriented for shadow. | - | - = G—E | = | F-à P , | # # ciº NATE CARD H § | D–H g | E 10 | : I | C—E | = | | E B—= 8 7 || 6 5 4 3 2 A = alºlºlºlº'ºlulululululuuluuluululºs MARG|N Plate 45. Using the Photo Coordinate Card. 60. The Photo Coordinate Card. It is difficult to indicate the location of objects on an aerial photograph because of the lack of names of a grid system. Location is therefore indicated by means of a coordinate card especially designed for use with aerial photographs. The method, in general, of handling the card is the same as that for using the coordinate cards in map reading. The card is divided into inch divisions, and each division is subdivided into tenths. The horizontal divisions are given numbers, and the vertical divisions are identified by letters. This is done in order not to confuse them with map coordinates. The left-to-right reading is always given first, followed by a dash and the bottom-to-top reading. The combined figure is inclosed in parentheses, AERIAL PHOTOGRAPHS 63 as in map coordinates. Plate 45 shows the proper use of a photo coordinate card, the coordinates of point “P” being (6.4-E.9). Single aerial photographs and uncontrolled mosaics reproduced by the lithographic process as photomaps will normally have a coordinate control system in accordance with the Atlas Grid as specified by Paragraph 28, AR 300-15. Controlled mosaics reproduced as photomaps will be equipped with the standard military grid. In the ab- sence of a coordinate card photograph coordinates can be read with any ruler graduated into inches and tenths. Measure the distance across from the left edge, and then the distance up from the bottom, expressing the major divisions of the last measurement in letters. 61. The Atlas Grid. Because of variations in scale, other inherent inac. curacies, and the difficulty of locating grid lines, the military grid is not used on ordinary aerial photographs. Instead, an arbitrary grid, known as the Atlas Grid, is employed. In this system, the grid lines are always 1.8 inches apart, regardless of scale. With this interval the grid lines are 1000 yards apart on a 1:20,000 photo. (1.8" x 20,000 =36,000"). The lines are numbered (1, 2, 3, etc.) from the bottom up but are lettered (A, B, C, etc.) from left to right, starting on the left. Therefore the coordinates of the origin (lower left-hand corner) are (A.O-1,0). The coordinates of a point P might be (C.2–4.8). The Atlas Grid may be overprinted on the aerial photograph. 62. Characteristics of Features. The identification of objects on an aerial photograph may be effected through four means, as follows: a. The shape of the object. b. The tone in which it appears. c. The shadow it casts. d. Its apparent or relative size. 63. Shape. On a photograph taken from the ground or an oblique from the air, objects appear somewhat in profile as is customary for the eye to view them. However, on a vertical photograph they appear in plan. A knowledge of their characteristic appearance is best obtained by comparing the image on the photo- graph with the object on the ground as if viewed from above. 64. Tone. The shade of grey in which an object appears on the photograph is known as the tone of the image. It is due almost entirely to the amount of light which is reflected by the object. The greater the amount of light reflected toward the camera by the surface of an object, the whiter it appears on the photograph. A surface which reflects no light appears black on the photo- graph. The amount of light reflected depends on the nature and texture of the surface as well as the angle at which the light is reflected. Because of the effect of texture (illustrated by the nap of a rug), the tone of objects as they 64 MAP AND AERIAL PHOTO READING appear in an aerial photograph will often be quite different than expected from their color. 65. Shadow. Shadow is a most important factor in the interpretation of vertical aerial photographs. Often the shape of an object is more easily deter- mined by its shadow than by its image or its tone. Shadow may disclose the approximate height, number of spans, and type of a bridge; the height and even class of trees; the shape and height of buildings; and the depth of cuts, pits, and quarries. 66. Recognition of Features. a. Recognition and identification of features. The recognition and identification of features on an aerial photograph are easy. One sees familiar things, and sees them as they actually appear. Unlike the map, which resorts to artificial signs or symbols to represent ground fea- tures, the photograph literally provides a picture of the feature itself. For this reason, in order to read photographs skillfully and accurately, the reader must be familiar with the appearance and characteristics of original ground features. The photograph, being taken from above, shows features in their horizontal plan only. This is excellent for showing cities, roads, woods, fields, streams, and all the natural ground features. In the case of a feature whose special identifying characteristic is its vertical profile, such as a church steeple, factory chimney, silo, or water tank, its identity may not be apparent directly from the photograph. However, shadows, when present, often outline its profile on the ground and thus disclose its identity. Shadows by their relative length often disclose the relative heights of buildings and trees. On the other hand, when the buildings or trees are known or suspected to be of uniform height, the relative lengths of shadows cast indicate the direction and amount of ground slope, if any. -> b. The part played by color. The eye is very sensitive to color. Therefore, color plays an important part in our daily recognition of features. The aerial camera on the other hand does not record color but evaluates the things that come within its focus in terms of their light reflecting properties. Light- colored objects usually reflect more light than dark ones and therefore appear lighter on photographs. But all colors do not reflect light in the degree that one might expect, and the texture of a surface may have a greater effect upon its light reflecting properties than its color. Shadows reflect almost no light and therefore show up black on photographs and are very prominent for this reason. * c. Roads. Exposed earth reflects light well. Gravel and unimproved roads, paths, construction work, and newly plowed fields will appear quite light on aerial photographs. Improved roads may be recognized by their greater and more uniform width, and their more regular curves. Primary gravel roads AERIAL PHOTOGRAPHS 65 usually appear wider and often lighter than paved roads. Railroads are usually darker and narrower than highways, with long straight tangents and long easy curves. Plates I, VI, VIII, and IX contain various types of roads, and the last two contain railroads. d. Details revealed by the camera. Woods may usually be identified as such by their characteristic tree composition. They usually appear as dark patches, not only because they are of a darker color, but because each branch and leaf is casting shadows on lower or adjacent branches, leaves, or the ground itself. Though the camera may not record the individual shadows, it, nevertheless, is sensitive to the reduced light reflection of the area as a whole caused by the general prevalence of shadows. For this same reason tall grass with its longer shadows appears darker than short grass, even though to the naked eye there is no perceptible difference of color and the shadows themselves may escape notice. The camera is so sensitive to light that it records the differ- ence in the amount of light falling on reverse slopes as compared to forward slopes, even though the sun is shining directly on both. This is the case with the finger-type drainage area noted above on Plate III. A realization that the camera records all details in terms of light reflecting properties greatly facili- tates understanding aerial photographs. Plate VII, center, contains patches of thick woods, thin woods, scattered trees, grass land, and areas partly de- void of grass due to surface erosion. Plates X and XI also show various types of woods. In Plate VII, bottom, there appear some dark areas that are not woods but are the shadows of small clouds. Brush appears similar to light woods but may be distinguished by its sparse character and lack of height. e. Water as revealed by the camera. Bodies of water have a characteristic appearance appreciably lighter or darker than the surrounding land, depend- ing upon the amount of reflection from the surface at the time the photo- graph was taken. Clear water does not reflect light and therefore shows dark on photographs (Plate VII, center), but if the water is muddy the dirt particles in suspension tend to reflect light, and the water will appear grey and at times quite light. The trace of streams that cannot be directly seen may be identified by their characteristic pattern and by the more luxuriant vegetation along their courses. Plate VII, top, shows a winding stream with sandbars at the bends. It also shows a primary highway and bridge. Plate X shows a characteristic drainage pattern. Plate XI shows minor drainage of various types. In the upper left are minor drainage lines through cultivated ground; in the left center one can see a small stream bed passing through grass land, probably a pasture; in the right center are wooded stream lines passing through a lightly wooded area; at the upper right are artificial drainage ditches in a cultivated stream bottom. Incidentally, the upper left corner 66 MAP AND AERIAL PHOTO READING of this particular photograph shows with unusual clarity the terracing of cul- tivated slopes. Such terraces are to prevent soil loss through erosion, and they run at right angles to the direction of slope. Thus they have the characteristics of contours, and as such clearly indicate ground forms. Swamps and marshy ground have a characteristic blurred appearance. When wet they are usually darker than the surrounding ground. f. Minor details. The identification of minor detail depends primarily upon personal familiarity with the characteristics of the original features. On Plate IV the military reader would easily identify as such the trench system in the center of the plate. He would also quickly recognize the four light spots at (0.75-B,60) to be an artillery firing position, because of the arrangement of the spots. The guns themselves cannot be detected, but the four white spots are peculiar to bare earth exposed by the muzzle-blast of field pieces. Like- wise, the dark objects at (2.6-A.3) are characteristic of motor vehicles halted off the road. Fences are inferred from hedge or section lines, outlines of cultivated fields, and the proximity of paths, trails, and roads. A good reading glass brings out a wealth of detail and is a great aid in studying photographs. NEGATIVE--" i *—F f = FOCAL LENGTH ! ENS A * = FOCAL LENGTH – H= HEIGHT OF PLANE GROUND 0 t & 0. º I tº Plate 46. The Relation of Scale, Focal Length, and Lens Height. 67. Scales. The vertical aerial photograph may be considered a map since all features on the ground such as roads, streams, woods, and towns are shown in their relative sizes, distances, and directions from one another. To use the photo as a map we must have a scale in addition to the direction of magnetic AERIAL PHOTOGRAPHS 67 north (Par. 59). The several methods of obtaining the scale of a vertical aerial photograph are as follows: a. By focal length and altitude. From Plate 46 we see that there is a direct relation between the focal length of the camera, the height of the plane, and the size of the photograph and the ground distance A-B. If the focal length of the camera is one foot and the altitude of the plane 1000 feet, then the photo- graph will be 1/1000 of the ground size. In other words, the R.F. (Par. 17) will be 1/1000. Expressed as a formula we have: focal length in feet height of plane The altitude at which the photo was taken and the focal length of the camera are ordinarily marked on it. (Par. 58.) The altitude given is the elevation above sea level. If the average elevation of the ground is much above sea level, allow- ance must be made for this fact. R.F. = Example: Focal length of camera: 6 inches (% foot) Altitude of plane : 12,000 feet above sea level Elevation of ground : 2000 feet above sea level I 1 R.F. = % & 12,000-2000T 20,000 Due to various factors this method of determining scale is only approximate. It will serve in most situations, but if an accurate determination is required one of the methods outlined below should be employed. b. By comparison with map. When a map of the area is available, the scale of the photograph can be easily determined. It is ascertained by finding the ratio existing between the length of any line on the photograph and the corresponding distance on the ground. The photo distance is measured on the photograph with a ruler. The ground distance is determined by normal map reading methods. For example, we wish to determine the scale (RF) of Plate II, using the map preceding the photo plates for data. The line from the crossroads at (16.8-19.8) to the crossroads at (18.3-18.5) on the Sandstorm Road is selected as the datum line. The straight-line distance between those two points measured on the map by means of its graphic scale is found to be 1990 yards or 71,640 inches of ground distance. The same line located and measured on the photograph measures 5.04 inches. Therefore we know that 5,04 inches on the photograph is equivalent to 71,640 inches of distance on the ground. Dividing by 5.04, we find that one inch on the photograph repre- M. and A. SIM. 68 MAP AND AERIAL PHOTO READING sents 14,200 inches on the ground. The representative fraction of the photo- graph is therefore 1:14,200. Datum lines selected for the purpose of making scale computations should be as long as possible, and preferably should pass through the center of the photograph rather than along an edge. When accurate results are desired two or more different lines should be used and computed, and the average of the separate computations determined. PLATE IT ORIENTED TO CONFORM WITH MAP Plate 47. Determining the Scale (RF) of a Vertical Photograph by Means of a Ground Distance Secured from a Map. c. From the ground. The scale (RF) of an aerial photograph can be determined from the ground itself whenever a map is not available. The scale of the photograph shown in Plate I would be determined in the follow- ing manner. The main road from the crossroads at (7.20-A53) to a point at (1.31-A.28) where the small curved trail joins the road is selected for the datum line. Measured on the ground by means of an automobile odometer, it is found to be 2.61 miles. The same distance measured along the road on the photograph in inches is found to be 7.34 inches. Therefore, 7.34 inches on the photograph equals 2.61 miles, or 165,369.6 inches, on the ground with the result that 1 inch on the photograph equals 22,530 inches on the ground. The scale (RF) of the photograph would therefore be expressed 1:22,500. The ground measurement could have been determined by pacing, by using a tape, or by any other means. (See Plate 48.) d. Making a reading scale. A scale expressed in representative fraction AERIAL PHOTOGRAPHS 69 form is of little value in making measurements of distance. For this purpose a graphical reading scale is more serviceable and should be constructed. A reading scale of 1000 yard units is the most convenient. The scale of the photograph in Plate II was determined (in b above) to be 1:14,200. This means that one inch on the photograph equals 14,200 inches on the ground. One thousand yards is 36,000 inches. 1:14,200 = x : 36,000 14,200 x = 36,000 x = 2.54 A line is drawn on the margin of the photograph and divided into 2.54-inch divisions, each of which represents 1000 yards of ground distance. The left division is then subdivided into tenths to represent 100-yard distances. PLATE I Plate 48. Determining the Scale (RF) of a Vertical Photograph. The Ground Distance Was Determined by Measurement of the Ground. A photograph coordinate card, divided into inches and tenths of an inch, provides a convenient reading scale based on inch units. In the case of Plate II, whose scale (RF) was determined above to be 1:14,200, this would be done as follows: 1 : 14,200 1 inch = 14,200 inches 1 inch = 394 + or 400 yards The photograph coordinate card may be used for both locating features and for measuring distances. 70 MAP AND AERIAL PHOTO READING 68. Azimuths. We are familiar with the three kinds of azimuth, i.e., grid, true, and magnetic (Par. 28). The azimuth measured from the grids of a map is of course grid azimuth. If an aerial photo is gridded, the same methods used with maps can be applied. If the photo is not gridded, as is often the case, all measurement of directions should be in magnetic azimuths. Thus compass readings in the field and azimuth readings on the photo will correspond without any need to consider true north or grid north. a. Determining magnetic north. The problem is to determine magnetic north on Plate II. The line from the crossroads at BM 346 (162-19.3) on the map (see insert preceding the photo plates) to the nearest water tank on Ebbert Hill (18.8-197) has a grid azimuth of 81% degrees as read from the map with *-ºmmº- sº gº * 2^T 3: 9 /* T. H. / !; B NA £ !d O 346 / ! { O) ; | WATER TANK \ \ # * ~ -º PLATE TI l Plate 49. Determining Magnetic North. (Diagram Oriented to the Photograph.) a protractor. From the orientation symbol on the map, we find that this is a magnetic azimuth of 81 degrees (to the nearest half degree).” The two points referred to are identifiable on the photo; draw a line on the photo connecting these two points. Now place your protractor with the 81-degree reading coin- ciding with the line. The magnetic north line is the line drawn along the base of the protractor as shown in Plate 49. It is obvious that with the pro- tractor oriented in this manner, the magnetic azimuth to any other point on the photo can be determined directly. If no map were available, the same method could be followed by using two points on the ground which are visible from each other and which can be easily identified on the photo. The mag- * The student must realize that the difference between grid and magnetic azimuths is often much greater than the #2 degree in this case. See Paragraph 31a. - AERIAL PHOTOGRAPHS 71 netic azimuth of the line connecting the two points on the ground would in such case be determined by compass reading. b. Making other azimuth readings. Once the direction of magnetic north (zero azimuth) has been plotted on the photo, the azimuth of any other line can be determined by usual map reading methods. Prolong the line whose azimuth is desired until it intersects the zero azimuth line. Then read the azimuth directly with the protractor. If the zero azimuth line on the photo is not conveniently located, it is a simple matter to draw a convenient line parallel to the zero azimuth line (Plate 49). It is not essential that there be a zero line in order to make azimuth readings. If the line whose azimuth is desired intersects the line whose azimuth has already been determined, the protractor can be oriented by placing it with the known azimuth reading on the known line and reading the azimuth of the other line directly from the protractor scale. ~ KNOWN S. AZIM UTHS (3. ,” & / 261° | O © --> Uz | |x\r . © | 22 D | SL" | 2^ º B A. Plate 50. Measuring Photo Azimuths. (Diagram Inverted to Approximate North Orientation.) c. Methods illustrated. Plate 50 demonstrates various methods of making azimuth readings. A datum line of 81 degrees azimuth (and therefore 261 degrees back azimuth) has been determined and plotted, and a north line plotted therefrom. (1) w. The azimuth of the line A-B is 144 degrees determined by con- structing a new north line through A and orienting the zero of the protractor thereon. (2) x. The azimuth of the line A-B is 144 degrees determined at the inter- 72 MAP AND AERIAL PHOTO READING section of A-B with the datum line. The protractor is oriented by placing its 81-degree mark on the datum line. (3) y. The azimuth of the line C–D is 229 degrees determined at the intersection of C-D with the datum line. The protractor is oriented by placing , its 261-degree mark on the datum line. (4) z. The azimuth of the line C–D is 229 degrees determined by ex- tending it until it intersects line A-B, whose azimuth has previously been determined to be 144 degrees, hence back azimuth of 324 degrees. The pro- tractor is oriented by placing its 324-degree mark on the line B-A. d. Plotting azimuths. In order to plot an azimuth it is necessary to have for a base a line of known azimuth at the point from which the new azimuth is to originate. A north (zero) line can be erected through the point by orienting the protractor to a known datum line and sliding it along the line until its base line, extended if necessary, passes through the point. Or, a line can be drawn into the point and its azimuth determined as in c and d above. The azimuth or the back azimuth of this line will then serve for orienting the protractor. | Plate 51. Plotting Photo Azimuths. Plate 51 demonstrates various methods of plotting photo azimuths. A datum line of 81 degrees azimuth and a north line based thereon have been deter- mined and plotted. (1) An azimuth of 40 degrees is to be plotted from A. A zero base line is constructed through A by sliding the protractor along the datum line with AERIAL PHOTOGRAPHS 73 a reading of 81 degrees until its base line passes through A. The protractor is then moved to and oriented at A and an azimuth of 40 degrees is plotted. (2) An azimuth of 252 degrees is to be plotted from B. A line is drawn from any convenient point on the datum line to B, and the azimuth (123 degrees) and back azimuth (303 degrees) of this line determined by methods previously covered. The protractor is moved to B and oriented by placing its 303-degree mark on this line, and the desired azimuth of 252 degrees is V". plotted. 69. Military Terrain Features. a. General. A successful commander is the one who most skillfully utilizes the favorable features of the terrain, and who also knows the unfavorable features so that he can make proper plans to avoid them or to minimize their effect. In general, the most important military features of the terrain are the road net, the wooded and open areas, and the basic tactical relief. A good military map shows all these features. However, with regard to the first two, they are constantly changing. Old roads are improved or abandoned, and new roads put in. Woods are cut down for lumbering purposes or converted into cultivated land. Land formerly culti- vated is often abandoned and soon grows up into brush and woods. A good map shows these features as they were at the time of the compilation of the map, but many important changes may have occurred since its compilation. Fortunately, these two types of features, roads and woods, are clearly and unmistakably shown on aerial photographs, being the most easily read features on them. Therefore, in the items in which the map is least trustworthy, the photograph is especially clear. The photograph does not show relief as clearly or in such detail as does a topographic map. However, the relief of an area is not subject to pronounced change over a period of years. Accord- ingly, in the one item in which the photograph is weak the map can still be depended upon. The map and the photograph, used in conjunction with each other, provide a most reliable means of studying the terrain. The map furnishes names and relief data, while the photograph provides up-to-the- minute data on existing roads, woods and open areas. b. Roads are very prominent on aerial photographs, and the details of the road net are quite apparent. From a military point of view, more must be known about roads than their location and pattern. Information concerning the nature of the road itself is desirable. Improved roads are generally wider than unimproved roads, and their curves are more regular and gentle. Main improved gravel roads are usually wider than paved roads. Oiled or tarvia type roads show darker than those made of concrete or gravel. Old concrete roads are darker than dirt or gravel roads because of the oil drip from the motor traffic, and in photographs taken at low altitudes the double oil drip 74 MAP AND AERIAL PHOTO READING streaks of the two traffic lanes can often be detected. Unimproved roads are narrow and irregular in width and follow a much more erratic course than improved roads. This is due to the necessity of avoiding steep grades in their construction. They often follow slopes in an angular fashion and pass around hills, spurs, and draws. Plate IX shows several highways and a railroad converging toward a city. The roads at the lower left and lower center of the plate are obviously old roads as they show many houses along their route. The road across the center is a wider road and for this reason probably a main highway. It is very recent because as yet it has practically no houses along its course. From its general trace, it appears that it must be a re-routing of the older road. The road across the top is also wide, probably a main primary road, and from its numerous houses is not a new road. Plate VIII also shows several roads, both primary and secondary, and also the darker course of a railroad. The un- usually wide road at the top center with its “fuzzy” edges suggests that the cuts and fills, the borrow pits and waste piles, and perhaps the ditches along the side are still bare earth and not yet grown over with grass or weeds. It is probably a recently completed improved dirt or gravel road and, in fact, may still be under construction. Incidentally, it is in a valley following along a stream line while all other roads in this area seem to follow the crests of ridges. On Plate I at (2.35-A 55) the “needle eye” formation is charac- teristic of a place in a road so poorly constructed that, on occasions, traffic must detour, thus forming by-passes. Such detail is invaluable in disclosing the nature of roads. From this one item one can deduce that this road may at times be very bad, and that it should be reconnoitered before being used. Such information can never be secured from maps. c. Woods are important military features. On aerial photographs they ap- pear as dark masses of irregular outline. Woods in front of positions obstruct fields of fire of the defense, and offer covered avenues of approach for the attack. Woods in the rear areas afford concealment for reserves, supply points, command posts, train parks, and similar installations. Therefore, the location and the extent of the wooded area are essential military information. It is also desirable to know the nature of the woods. Woods consisting of mature trees so closely spaced that the branches interlock (Plate III, right center) have vastly different military value from woods whose trees are so spaced that much of the ground is clearly visible (Plate III, lower right and lower left center). Maps do not generally show this distinction, but it is clearly evident on aerial photographs. The seasonal characteristics are reflected in photographs. Evergreen forests shown dark and dense in all seasons. d. Relief. Relief is not as easily read from aerial photographs as from AERIAL PHOTOGRAPHS 75 topographical maps. Nevertheless, aerial photographs contain much informa- tion regarding the basic relief of an area. Good shadow values often picture the relief of the area directly, as is the case with the finger drainage on Plate III, and also in portions of Plate IV. Also, the relative lengths of shadows of buildings and trees of similar height often disclose the direction and the amount of slopes. Terracing, when present, is a clue to relatively rugged country, and can often be seen in photographs as in Plates VIII, IX, and XI. To all intents and purposes they can be considered as form contours and serve as such for indicating relief. Bends in the routes of unimproved roads where they pass around ridges, spurs, and draws, are likewise valuable clues to relief. The most valuable source of information regarding relief, however, is the drainage net, which can be clearly followed on photographs. Relief, that is, the valleys and the ridges, is the result of water erosion. The streams carve out the valleys, and every stream line discloses the location and the direction of a valley. Between any two adjacent streams there must be a ridge line, and its location and direction must conform to the two streams between which it lies. * Streams, or drainage lines, follow definite natural laws and for this reason have easily recognizable conventional patterns. Plate X shows a typical drain- age pattern. Plate XI shows various types of minor drainage and their characteristic patterns in various types of background terrain. In both cases the patterns of the drainage lines are clearly marked by the more luxuriant vegetation along their courses. They can be traced out on the photograph, or on an overlay, and will furnish the pattern of the low ground of an area. By placing a form ridge between each two adjacent stream lines, its location approximately centered, and its direction conforming to the stream lines, one will have a pattern of the ridge framework. Such a framework will not perhaps be exactly true to the ground in all details, but the picture it presents of the general location, direction, and extent of the ridges with their lateral spacing will be a reliable picture of the basic terrain structure of the area. The location, direction, size, and extent of the terrain corridors and cross- compartments thus disclosed can be relied upon for planning tactical opera- tions. You do not have to have elevations in feet for these purposes. On Plate VIII it is easy to see that the drainage lines all run away from the village. From this it is evident that the village is situated on high ground. Further study of the stream lines shows the village to be on a ridge, and that the main transverse highways and railroads follow along this ridge. The tactical significance of such information is valuable. The higher buildings of this village should offer good observation points and overlook much of the surrounding territory. Also, the roads, being on a ridge, can probably be seen 76 MAP AND AERIAL PHOTO READING from quite a distance, and troop movements thereon by daylight could be observed by the enemy. Plate 52 shows a tracing of the drainage system of Plate XI. Plate 53 shows the ridge lines added, based on the drainage system. sº sºme • * ~” ( ^_^ The combined plotting discloses the basic terrain structure of the area. It does not show the details of the minor relief nor the relative heights of the _7. ~ – ‘’’ Yº ~...~~ N- ~. & j- º, y - \ -> | 2TS_ ge º e’ ~ * * Plate 52. Basic Terrain Structure. (Drainage lines traced from the photograph.) sº gº - - - + = . .” | _- – ...— ” | - Ç * \\ 11" =% –“ N 32° 2 W \!' S. %uulutiºnſ %, nº!" '^2 / / / / / / / / T- Z º % ~...~~. // | 1 ||' */2, ~ *= / ~/ // " ^ Z/2 s % ,11” * Z, , ". * Aº I l ** * * ~! tº *s e * 2 | * e’ .' itſ l'' | s 2 /* \\ / / / / / /////////// all" - §2. \\\ ſ 1, 1 '' // / / / / / / / / / / s º, \\ | I *s 2w \\ – ‘’’. 11' ,-s *s 22 ſº || | * © s 2. ~, | —" ſº \ *s 2. ^, | | | ) lſº I l V * * | º 2. 22. A)', W * | | | | | | & \\ S * \ | | \ 2^ 2. A \" / | 1 V s º 2. // ſº \ \' wº = S3 TN. . ." tunn W. \\\ F- wº' 2 : % tº v \\ T- * 2. ." \ T- -_ 7- 2 •. ‘’, w) \ T- - .” 2 /, ///////. g // 1 \\\\ ////, *e +. *. -- 2,11' f / | 1 || 1 || 1 | ^^zz, " J. Z - - - T- ~1' --" 2 TS- * \ = \ *. > -- ~ * Plate 53. Basic Terrain Structure. (Ridge lines added by inspection based on the drainage traced in Plate 52.) AERIAL PHOTOGRAPHS 77 ridges and hills. These data, if needed, can be determined through stereoscopic study. 70. Stereoscopic Study. Our visual appreciation of relative distances depends upon the slightly different view of various objects presented by each of the two eyes. If two photographs of an object are taken to the same scale from two different camera positions as in Plate 54, and both pictures are viewed, each by one eye, but simultaneously, the appreciation of distance or elevation becomes possible. This is because a different view is presented to each of the two eyes as in ordinary vision. To obtain a combined or fused image, these conditions must be satisfied in the arrangement and viewing of the two photographs: a. Both pictures should be equally legible. The photographs should there- fore be equally distant and equally illuminated. b. The photographs should be arranged with respect to each other and the observer's eyes so that the exposure conditions are restored. c. The photographs should be oriented so that the shadows fall away from the source of light. This principle is employed in the stereoscopic study of aerial photographs. CAMERA RAYS-sº- ––object sº a Plate 54. Diagram of a Stereoscopic Pair of Aerial Photographs. 71. Stereoscopes. The stereoscopes used for interpretation of aerial photo- graphs may be classified as mirror, lens, or prism types. The mirror type has a large field of view and is very adaptable for general military use. The lens 78 - MAP AND AERIAL PHOTO READING - stereoscope, which may consist simply of spectacles, has the advantage of magnification. The prism stereoscope is of particular use for examining T-3A photographs as it permits a wide separation of the two overlapping photo- graphs. The stereoscope itself is not necessary for stereoscopic vision. It is only a convenience. Stereoscopic effect is obtained when one eye sees one picture only, and the other eye sees the other picture. Plate XII shows a stereoscopic pair, or pictures of the same area cut from the overlapping portion of succes- sive prints, arranged and spaced for use without instruments. Place the plate on the desk about 14 to 18 inches from the eyes. Hold a piece of cardboard vertically between the two pictures so that each eye can see only its respective picture. Permit the eyes to relax somewhat; do not concentrate or stare. Con- tinue to look at the pictures, and the stereoscopic effect will develop. Some persons may have to try several times before they get the knack, but nearly everyone attains it with practice. The same effect can be attained with no aids whatever. Focus the eyes on some distant point, 20 feet or more away, and relax them (day-dream). Move the plate into the line of vision without permitting the eyes to look directly at it or to focus upon it. Rather, look through the plate in a dreamy manner. After several tries the stereoscopic effect should develop. 72. Procedure for Stereoscopic Examination. The following procedure should be observed when making a stereoscopic examination of aerial photo- graphs: a. Take a stereoscopic pair of vertical aerial photographs and by means of their collimating marks determine the principal or center point of both. b. On each photograph mark the point corresponding to the center of the other photograph and draw a line between it and the center of the photo- graph. This line must be held parallel to the eye base while the photographs are viewed by means of a stereoscope. c. Take the two photographs and orient them in the direction of flight so that the overlapping detail common to both is roughly in coincidence. Note the direction of shadow. The shadow should fall toward the observer; if not, turn them about 180 degrees and reorient them as before. d. Place the photographs under the stereoscope so that the left print (taken by the camera on the left of the overlap area) is observed by the left eye and the right print by the right eye. e. Shift the photographs so as to bring the two lines drawn between the corresponding center points parallel to the eye base and in prolongation with one another in the center of the field of view of the stereoscope, AERIAL PHOTOGRAPHS . 79 f. Without changing the relative position of the lines drawn through the corresponding center points, bring together or separate the photographs until stereoscopic conditions of fusion are best fulfilled. This may be facilitated by placing one finger over points of corresponding detail on each photograph and by varying their separation, first fusing the fingers. g. After a little practice, photographs may be correctly oriented without ac- tually drawing the lines of centers, which mar the photographs. 73. Summary. To obtain a reasonable knowledge and proficiency in Aerial Photograph Reading, the combat officer should strive for: a. Knowledge of the various types of aerial photographs. b. A basic conception of the effect of altitude upon detail registration and amount of area. c. An understanding of the data furnished in a legend. d. An understanding of the use of the photo coordinate card. e. The recognition and correct evaluation of roads and road nets. f. The recognition and correct evaluation of various forms of vegetation in so far as they may afford cover and concealment or affect fields of fire. g. The ability to plot the outline of a photograph onto a map by inspection, that is, the recognition of terrain detail along the edges. h. The ability to compute the scale (RF) of a photograph by any of the following means: (1) Focal-length and altitude. (2) Ground data secured from the map. (3) Ground data secured from the ground. i. The ability to construct a graphic reading scale. j. The ability to secure azimuth orientation data and to perform azimuth computations. k. The ability to trace out the drainage system and therefrom to grasp the basic terrain structure. l. The ability to compare the photograph and the map as to essential military features and to detect any such data appearing on one that is not substantiated by the other. m. A knowledge of the operation, capabilities, and limitations of the stereoscope. Questions and Exercises 1. With reference to aerial photographs, define the following terms: a, Ver- tical. b. Oblique. 2. What is the finished size of the standard single-lens individual print? 3. What is meant by the “legend” on a photograph? 80 MAP AND AERIAL PHOTO READING 4. What data is usually shown in the legend? 5. Describe the nature of the object at or passing through the following location: (Use photo card issued with this text). - a. Plate I (7.0-B.6) b. Plate I (62-D.6) c. Plate I (3.0-D.3) d. Plate I (4.5-B,8) e. Plate I (1.5-D.8) f. Plate I (0.3-D.0) g. Plate II. The dark streak at (4.00-B.25) h. Plate II. The semicircle at (3.45-D.10) i. Plate III. The line of dark objects at (4.22-B.53) 6. Describe the nature of the terrain, with special reference to vegetation, in the general vicinity of the following points on Plate I: a. (4.0-B.5) b. (42-D.4) c. (6.5-E.1) d. (25-E.1) e. (65-B3) f. (5.5-B.0) g. (6.6-C5) 7. Study carefully the detail shown in Plates I, II, and III, and then by comparison of detail state your opinion of the scale of each of the following plates: - Plate IV Plate X Plate VIII. Plate XI Plate IX 8. Presume a vertical photograph shows the following legend data: “(8.25- 11,500).” What is the scale (RF) of the photograph? 9. On Plate VIII a straight line from the road junction at (0.92-C.58) to the road junction at (5.93-C.70) was plotted on a 1:20,000 map, and determined to be 5.6 inches long on the map. a. What is the scale (RF) of the aerial photograph? b. How many yards (to the nearest full hundred) of ground distance will be represented by one inch of photo distance?. 10. On Plate IX the distance measured along the main roads from the cross- roads at (0.37-D.73) to the road junction at (6.62-A.72) is 2.6 miles. a. What is the scale (RF) of this photograph? b. What would be the length (inches to two decimals) of a 1000-yard divi- sion of a reading scale for use with this photograph? AERIAL PHOTOGRAPHS 81 11. On Plate IX the magnetic azimuth of the line from the road junction at (3.26-B.75) to the road junction at (3.86-E.12) is 31 degrees. a. What is the magnetic azimuth of the line from the road junction at (6.62-A.72) to the lone building at (0.88-D.30) P b. A patrol in the field noticed the schoolhouse (center point) at (0.83-D.65) on Plate IX, determined its direction to be 294 degrees magnetic azimuth, and estimated its distance to be 2900 yards. What was the location of the patrol at the time it took the reading? (Use a scale of 1 inch equals 600 yards.) 12. Compare Plate I (photograph) and the map (insert preceding photo plates) as to the road net through MAXEY RIDGE (17-18); RIVET RIDGE (17-18); SINGLETON HILL (18-18); RILEY RIDGE (18-19). 13. Compare Plate I and the map as to the woods from the 30th INFANTRY WOODS (18-19) to the 7th INFANTRY WOODS (19-18). 14. Compare Plate I and the map in regard to the woods on DAVIDSON HILL (19-19). 15. Name the various clues appearing on aerial photographs which convey information regarding the relief of the area. 16. Which of these is the most valuable in disclosing the basic terrain struc- ture? 17. What is a stereoscope and for what purpose is it used? 18. What photographic material is needed for use with a stereoscope? |- - - - º º - _ ºf 3.2° - - º - * - - Ž Pºstol ºange > * 27. sº-sow : º 2 - - - - - - - - &: \ º º | º 2. § 2. : - º - º - ------------ *—- º: * , º **s-----zºº - - - - º º -zºº - | C ºn |- --- º -- - N = º - º sº º - -- º-º | | ºs- - - 7TH | º - s -- º: N. º - - - - - - Nº. - * - - - *. - G - h º * , O) º | - --- º infantry " | D5. º \º - -o-o- --~~~ Plot Map of Photographs Shown in Plates I, II, III and V. ... ºl. ººl sº- ºf DES hº º Tºº º tº ºf º - º * sº Nº Tº…I.ſ 777. Tº |\ ºt. Fº Qºl-ſº 3-O- º sº º º ſº º/unfºrty -- ºf sº tº ºf Akrºy woods --- º ºf . --~~ *-R-- – - Nº 2 / ******Nº, º - º/ woodºº/* N º ſº º | (Holliday Hill º Hiſºlº -- - º º º : oic-i-ario- 1932 aw-u---G-ET1- cº-awak tº D-cº-º-º: '000'， :I \Ideu 3040 quae teoſquºA. "I øjet， Aturav -s ºn ºsºitoo u ſvº aeq. ohou， '000'ſ I:I º qdeu ºoyou）ſ leoņiºA ‘II ºffeldſ Aſulaev -s ºn ºsduo o uſv ſſol o notieſ |-99†7€2I '000'g: I º qdeuſão, ou， leoņuºA ‘III ºſťIJI aeuuw 's 'n "sólido utw ſą d¡olae “qdeuffoqoqae Iºoſſaeº. A "AI øſt-I-I Aſuluw ‘s ºn ºsduoo u ſv aeq oqo， ºnºaj 000€ ºudeuffonoqae ºnb11q0 A 94 elae Aturav -s -n 'saeuoo u ſv. ae omotae Photo by Air Corps, U. S. Army º º º Plate VI. Oblique Photograph. 5000 feet. Photo by Air Corps, U. S. Army Plate VII. ae /.99†?€.2IO *II. A ºſtel， "XI ºſtriae Atuurwr ºs ºn "ºdroo aev ſo ſynona Photo by Air Corps, U. S. Army Plate X. Typical Drainage System. ººeuſe101 10 upIAI J0 sºđAL ‘IX ºffeſ， Attuae ºs ºn ºstroo u ſv. Ka onou a U. S. Army Photo by Air Corps, Stereoscopic Pair. Plate XII. CHAPTER IX APPENDIX 74. General. The following paragraphs are added more as a matter of gen- eral information regarding maps and their construction than as being essential to practical reading of military maps. 75. Marginal Information. Maps usually have a mass of detailed informa- tion on their margins. This text has already discussed those of particular value to the map reader. However, some of the items listed below may also be of interest: (The numbers below in parentheses refer to Plate 55.) a. Geographic Index number of the map and the location in the Geographic Index of the quadrangle shown on the map sheet (1). Directions concerning the use of the Geographic Index system are explained in Paragraph 82.) b. Descriptive title, giving the name of the state or states within which lies the area represented and the name of the area or the map quadrangle (2). c. Representative fraction of the map and three graphic scales, one in feet or yards, one in meters, and one in miles (3). (Only one graphic scale is re- quired on maps not intended for lithographing. Usually there are two scales, one in yards and one in miles). d. True meridian, magnetic meridian (and variation with date and rate of change), and grid meridian (4). - e. An explanation of any symbol used which is not prescribed in Basic Field Manual, FM 21-30. f. Contour interval, when map is contoured (6). g. Name of the organization which issued the map (7). A. Date of issue or revision (8). i. Names of organizations executing the surveys and topography upon which the map is based and date of their execution. If the map has been compiled from other maps, source of compilation is also shown (9). j. Name of the projections used (10). k. Horizontal datum (11). (If no horizontal datum is given, the latitude and longitude of at least one point shown on the map and easily identified on the ground and the method of its determination.) l. Vertical datum (12). m. Zone of the military grid (13). m. If the area represented lies in the overlap of two grid zones, a reference to the grid of the second zone (14). o. Designations of the geographic grid lines (15). p. Designations of the military grid lines (16). 95 96 MAP AND AERIAL PHOTO READING H + || +| -#-+ @–Ģ+-Oº8|| §4} ------# —@ ++ ++ +-9f99! ~ | +- –|- +-|- - –|—O98|| - H– +- |- |-#|- º” x=Nozayo (€)* (1）)-FT77777777„$$|-——G) @*@3T0NVMQvno "Egny-ıSIXSI/OOZZM-OO6CNdvW TVOLLOWL**） CNVTWMVWò^^ºv Sºn 'SMEENIONE JO sego5*@ \o : Lines of al geo- graphic glid º i + + -- -R . + (13. Crosses!ond ticks of the militory grid of Zone B gº i oo'ºtsuocoo 625000 (Washington ond Vichy yºg/ 630 635 6&O 76°46’ Prepored under the direction of the Chief of Engineers, U.S. Scale Trias - 3 *. Army, 1919-1920. | O | 2 S M II.V.S. *… Control in part by U.S. Coast ond Geodetic Survey, surveyed - I - I - I - - . % in 1890, 1900 ond 1904-1906 in cooperation with the Stute "####-º-º-º-º-º YAR08 2. of Maryland. Hirarr; I # =} $_; KILortſ tº $ 9 Topography by Corps of Engineers, U.S. Army, 1920 Contour intervol 20 feet (6 |* West half of lower third reduced from U.S.G.S, mop of Wgsh- @ Ooſum is moon $ed ſeve/ @ º ichni? g o' ington sº vicinº, *::::: f sis º: !. FIVE TRºcus AND YARD GRID CCM PUTED FROM tºo (D Pelyconic Projection. North Americon Datum, (3): SYSTEM FOR PROGRESSIVE MAPS IN |= 15° 77° O” THE U. S." ZONE A., U.S.C. a. G.S SPECIAL. Žiž 30° PUSLtCAT IOR NO. 59. #? Non-stondard Symbols (T H E Las T T M Re E Otgif 5 Öf T tit º GR: O Muld ºtRS ARE O ºf . TT to) # (9)→LAUREL.MD ji * Sº & tº CŞGut |5 (GR to for zone e Ikolc AT Ed Alon 6 boſs otR, YALut? N- ***** G oic Areo in Four to Rrºt R & J. Søition of 1926. O biott off ICERS usuw G THIS MAP W IUL MARK HERE ON CCR" APPROK! MATE ME tº RECTION5 A80 ADDITIOMS which COME TO THEIR AT TEM" ©ECLºº TiOM 1026 110x AND MAIL bintct ſo "THE CHIEF Öf £NGINEER3, ANNUAL MAGNETtc. CHANGE 45° waºn itſ GT ON. O.C." trºgaº ſ S Plate 55. Marginal Data on Standard Maps. 98 MAP AND AERIAL PHOTO READING q. Names of the adjoining map sheets (17). r. An index of the adjoining map sheets (18). s. Filing name (19). ' NoTE. Frequently maps are prepared for temporary or local uses and are not intended to be included in any mapping system. Much of the above-listed marginal information would not be required on such maps and would there- fore be omitted. 76. The National Grid System. A nation-wide grid system has been de- vised, by which the location and the identification numbers of the grid lines for the entire United States are prescribed. Briefly, the United States has been divided into seven grid zones, designated from east to west as Zone A, Zone B, etc. Each zone is nine degrees of longitude in width and extends all the way across the country (Gulf to Canada) in height. The width allows for a one-degree overlap of adjacent zones. The center vertical grid of each zone is placed on the central meridian of the zone, and therefore is on a true north- south axis. The numbering of the grids of each zone is based upon the inter- section of this central y-grid with an x-grid tangent to the 40° 30' parallel of latitude. The y-grid (vertical) at this point was given the arbitrary grid number of “1000," and the x-grid (horizontal) the arbitrary number of “2000," and the other grids of the zone are numbered to conform. 77. Classification of Military Maps. A map is a conventional representation of a portion of the surface of the earth as a plane surface. Certain types of maps have been found to be most suitable for military purposes. A standard map is a geographic or topographic map ordinarily prepared in time of peace for military and general use. For military purposes, standard maps are classified as follows: a. Classification according to scale. Although the student may encounter the old terms, “terrain map,” “tactical map,” etc., maps are now classified more according to their scale, such as small scale, large scale, and medium scale maps. This is due to the fact that aerial photography is employed so extensively now in the preparation of military maps. The large scale map, say 1:25,000 or thereabouts, is valuable in tactical operations of small units, but for units the size of a corps, or army, a medium scale map would be necessary in order to cover sufficient terrain on one or two sheets of the map. For planning campaigns or for the operations of large units, a map of still smaller scale, say 1:500,000 would be advisable. There are also special maps ranging from air navigation maps to simple road sketches. b. Special maps. In addition to the above, there is a large number of special maps ranging from air navigation maps to road sketches (usually 1:20,000), area sketches (1:10,000), and military sketches (1:5000). These APPENDIX 99 latter types are often used for indoor tactical instruction when impracticable to use the terrain itself. 78. Logical Contouring. Any student who still has difficulty in reading a contoured map, namely in translating the contours into ground forms, may be helped by the following description of the method of placing contours on a map. Contours are placed on maps not through detailed surveying of each contour line but by a method known as “logical contouring.” The procedure is as follows: first, the area is surveyed, the location and trace of the stream lines and the ridge lines being carefully plotted. Then the elevations of the hilltops, certain points on the streams, and intermediate points where major changes of slope occur are determined by instrument. These points are called Y. f | 867 x 850 × 790 N l & * º * = .* ". 892 X 4 / X \ 42 865 • J f &P X 845 Plate 56. Basic Sketch Before Contouring. critical points. (See Plate 56.) Since the critical points whose elevations have been marked on the basic sketch were selected at the major changes of slope, it follows that the slope between any two adjacent critical points will be ap- proximately uniform. Therefore, the contours should be uniformly spaced. Small marks in pencil known as ticks are accordingly plotted between ad- jacent critical points, their number depending on the known difference of elevation. Thus on Plate 57 there have been indicated the ticks between the stream courses and the known elevations, for example, six between the 810 elevation near the stream and the 873 ridge point, and five between the 800 elevation near the stream and the 850 ridge point. The next step is to con- nect up the tick points with the contour line, beginning with the lowest eleva- tion and working uphill. Their trace conforms to the ridge and to the stream 100 MAP AND AERIAL PHOTO READING lines. This last step should be performed in the field so that the topographer can view the area being contoured and be able to adjust, by estimation, the actual trace and the spacing of the contours to conform to the minor changes of slope and direction. Plate 58 indicates the method of drawing in the contours to conform to the basic terrain structure. Plate 59 shows the com- pleted contoured sketch. As a final step it adds to clarity to accentuate the 800 and the 850-foot contours. ~4. | \ * . 850; / ſ *ºr. * - - t ! 892 ... * * 845 Plate 57. Method of Spacing the Contours. Plate 58. Drawing in the Contours. APPENDIX 101 79. Time-Distance Scales. When much work in determining distance and time of marches and movements must be done, it is of great convenience to construct a time-distance scale. Such a scale is in reality a graphic scale divided into time units instead of into distance units. Such a scale for use in connection with movements of foot troops (2% miles per hour) could be constructed as follows. From the miles graphic scale of the map draw a line to represent 2% miles which will therefore represent one hour of travel. ~–//5 ſº , º/, Plate 59. The Completed Contoured Sketch. Divide the line so drawn into twelve equal parts, each of which will then represent the distance covered in five minutes of travel time. To measure any given time-distance, use it exactly as a graphic scale, the full divisions representing full hours, and the subdivisions indicating the number of minutes of travel time. The scale might be divided into sixty parts, each representing One minute of travel. A time-distance scale for any other rate of travel could be constructed in a similar manner. - 80. Direction by Bearings. The standard method of indicating accurate direction, until the development of the azimuth system, was by means of “bearings.” In this system the degree is the unit of direction measurement, as in azimuths, and the direction is expressed by first indicating either north or south as the base direction, and then indicating a number of degrees to the east or to the west of this line. This method is seldom used in military map reading but may be encountered in joint operations with the Navy. The following are a few examples of bearings as compared to their respective azimuths: r 102 MAP AND AERIAL PHOTO READING Azimuth: Bearings: 250 North, 25° east. 150° South, 30° east. 2150 South, 35° west. 300° North, 60° west. 81. Slopes. The amount of slope between any two points on the ground (called grade in railroad and road work) can be indicated either in terms of degrees, per cent, or gradient. Average slopes for average purposes are usually measured with an instrument designed to measure vertical angles in degrees, called a clinometer. A slope of one degree would be a slope that rises at an angle of one degree from the horizontal, which would be one foot in a horizontal distance of 57 feet. For gentle slopes, and in cases where great accuracy is required, slopes are expressed in per cent. A one per cent slope is one that rises one foot in 100 feet of horizontal distance. The deter- mination of slopes is a factor in map making, but it is seldom encountered in map reading. The subject is covered more fully in Paragraph 30, FM 21-25. 82. Geographic Index. a. Decision has been made to supersede the Harriman Index as rapidly as practicable by the system known as the Geo- graphic Index. This will require several years as old maps with the Harriman Index will be retained until replaced. As each map of any part of the United States or its possessions, except historical maps, now in the files of any office of the Military Establishment, is used in the military service, it will be marked with the proper Geographic Index number for use in filing and cataloging. Each map of a permanent value hereafter prepared in time of peace by any organization of the Army will bear its Geographic Index number. Maps will be requisitioned by geographic index together with name and scale when ap- propriate. b. Index Symbol. The index symbol for each map shall consist of a series of letters, digits, and signs, to express first the latitude and longitude of that point which is nearest the equator and the Greenwich meridian (hereafter referred to as the “index point”); and, second, the extent of the area covered by the map away from that point. For these purposes the index symbol shall be constructed in the following order and manner, with the significance of each part as indicated: - (1) The letter N or the letter S, whichever is appropriate, to show whether the index point is in north or south latitude. (2) A series of digits representing the degrees and minutes of latitude of the index point, without separation and without degree and minute signs; only when especially required, fractions of minutes may be added. (a) For standard quadrangles, whose extent in minutes is the same for both latitude and longitude, the number of minutes shall be written only once, APPENDIX 103 (b) For special or irregular areas whose extent in minutes differs for latitude and longitude, the extent shall be expressed by the number of minutes of latitude, the letter “x”, and the number of minutes of longitude. c. This system provides for areas throughout the world, but the greatest ap- plication by the War Department will be in north latitudes and west longitudes which embrace the United States and most of its land possessions. Here all latitudes are north and all longitudes are west, and the southeast corner is closest to both the equator and the meridian of Greenwich. d. Examples of the application of this system to specific areas in north lati- tudes and west longitudes are given below: (1) The Searles Lake, Calif., 1-degree quadrangle, the geographic loca- tion of the southeast corner of which is at Lat. 35° 00' N., Long. 117°00'W. The index number would be N3500-W11700/60. (2) Standard quadrangles extending 30, 15, 7%, and 6 minutes in both latitude and longitude and having their southeast corners at the same loca- tion as in the preceding example would be numbered N3500-W11700/30, N3500-W11700/15, N3500-11700/75, and N3500-W11700/6, respectively. (3) An area extending 15 minutes in latitude and 30 minutes in longitude from a southeast corner located at Lat. 35° 30' N., Long. 117° 30'. W., would be numbered N3530-W11730/15x30 and other special areas would be num- bered in a similar manner. (4) The Kearney Park, Calif., 7%-minute quadrangle, the southeast corner of which is located at Lat. 36° 37' 30" N., Long. 119° 52' 30° W., would be numbered N3637.5-W11952.5/75. (5) The San Diego sheet of the Strategic Map of the United States, extend- ing 2 degrees in latitude and 6 degrees in longitude from a southeast corner located at Lat. 32° 00' N., Long. 114° 00' W., would be numbered N3200- W11400/120x360. e. All maps which are bounded by military grid lines will have either lines of longitude and latitude or tick marks indicating their location. These gridded maps will be indexed by interpolation and estimation. 83. Ridge and Stream Lining. This consists of accentuating the ridges and stream courses to make the basic structure of the terrain stand out. It is applicable to either maps or aerial photographs. In stream lining, the main streams should be emphasized by drawing over them a heavy blue line (either ink or pencil); tributary streams should be drawn over with a light blue line. Then the main ridges should be marked over, preferably in heavy brown lines with the minor ridges in lighter brown ridges. The ridge lines form a connected structure but never cross streams. For one who has difficulty in visualizing the terrain from the contours, ridge and stream lining offers 104 MAP AND AERIAL PHOTO READING an alternate method of studying the terrain. In any case it is of great value in terrain studies on maps or photos which are not contoured. 84. Care of Maps. Every user of a map should exercise care in handling it. Unmounted maps should be kept flat or rolled, not folded. Should folding be necessary, first mount the map on linen or similar cloth; then fold like a bellows to a convenient size with the printed surface out. The user can thus change from one area of the map to another with minimum effort and wear on the map. 85. Solutions To Exercises, Chapter II. 1. a. HOLLIDAY HILL (21-20). b. NALLE HILL (19–22). 52d INFANTRY WOODS (24-21). . OLIVER HILL (20.7-182). . 4th INFANTRY WOODS (17.8-185). BUMA HILL (23.5-20.8). RJ (22.15-22.48). . House (1892–21.60). Stream junction (24.83-21.28). . House (22.04-20.96). Railroad and highway crossing (20.57-20.99). . Narrow-gauge railroad. . Cemetery. c. Water tank. d. Bench Mark No. 48, elevation 375 feet. e. Swamp or marsh, wooded, 2. : 3. : 4. : 5. a. Road junction one-quarter mile (or 400 yards) northeast of Bench Mark 454 (24-21). b. Hill 500 yards north of JORDAN HILL (23-19). c. Woods on western slope of JOURNEY HILL (22-21). d. Woods 200 yards south of EBBERT HILL (18-19). 6. A Bench Mark is a surveying monument marking a spot whose elevation has been accurately determined. The correct symbol is a cross (diagonal arms) with the letters “BM” and the elevation. Sometimes the serial number of the Bench Mark is also shown. 7. a. Not inclosed in parentheses. Grid numbers in excess of the last two numbers not dropped. Both figures should read to the same number of deci- mals. Should be written: House (21.54-20.49). b. Coordinate figures in reverse sequence. Should be written: BM 415 (20.70-1873). APPENDIX 105 c. The “,03” of the second figure is incorrectly shown as “30”. Should be written: BM 422 (18.42-2003). This error would amount to 270 yards, as BM 422 is only 30 yards from the 20 grid line, not 300 yards. 86. Solutions To Exercises, Chapter III. 1. 2175 yards. 2. 3425 yards. 3. 3.33 miles. 4. 1 hour 20 minutes. 3.33 miles —– 2.5 mph = 1.33 hours. 1.33 hours = 1 hour 19.8 minutes = 1 hour 20 minutes. 5. a. The head of the column will stop for lunch at RJ (21.32-21.18). 11:30–8:47 = 2 hrs. 43 min. (travel time). 2 hrs. 43 min. = 2.72 hrs. 2.72 × 2.5 mph = 6.8 miles (distance). b. Head of column will arrive at 1:59 P.M. Total distance scaled on map is 10.5 miles 105 ––2.5 = 4.2 hrs. (travel time) 4.2 hrs. = 4 hrs. 12 min. 4 hrs. 12 min. + 1 hr. (lunch) + 8:47 (start) = 1:59 P.M. c. Tail of column will clear at 2:47 P.M. 2 miles (length of column) —–2.5 = 0.8 hrs. = 48 min. 1:59 P.M. –– 48 min. = 2:47 P.M. 87. Solutions To Exercises, Chapter IV. 1. a. 43°. b. 11.1% “. c. 207%%. d. 327°. 2. A road junction at (23.31-1932). 3. a. 2° 30' east (1935). 2° 40' east (1940). b. 2° 12' east. c. 26 minutes, or % degree, to be subtracted from the grid azimuth to get magnetic azimuth. 4, 279° magaz (279%* grid az— 4° adjustment). 5. At the center of the “O'” in LONG HILL (20.75-1993) 123° mag az–8° adjustment = 115° grid az 207° mag az—8° adjustment = 199° grid az. Grid azimuths of 115° and 199° plotted from BM's 471 and 449, respectively, intersect at the above point. 6. On top of a small hill at (1947-1900). 106 MAP AND AERIAL PHOTO READING 291° magaz—8° adjustment = 283° grid az 228%" magaz – 8° adjustment = 220% º grid az 283° — 180° = 103° back azimuth 220%" — 180° = 40%.” back azimuth The above back azimuths plotted from BM's 418 and 416, respectively, inter- sect at the above point. 88. Solutions To Exercises, Chapter VI. 1. : lows: . House: 440 feet. c. Stream junction: 367 feet. . Church: 336 feet. d. DAVIDSON HILL: 465 feet (approximate). . KELLEY HILL (22.83-21.67), 505 feet (approximate). . UPATOI CREEK at (1700-21.92), 195 feet (approximate). Spur. . Saddle. Draw. Hill. Draw. Spur. . Ridge. . Valley. . DAVIDSON HILL (1933-1941), 465 feet. Ridge at (20.63–1898), 392 feet. Saddle at (21.61-1898), 378 feet. Ridge at (22,07-1855), 390 feet. Road junction at (22.57-1769), 362 feet. . Stream at (20.08-1920), 328 feet. Stream at (21.33-1904), 341 feet. Stream at (21.89-1897), 342 feet. Stream at (2233-18.14), 297 feet. . Steepest up-grade (20.27-1929). . Steepest down-grade (21.28-1897). . Yes, disregarding all woods the observer can see the crossroads. . 413 feet, maximum permissible elevation of mask, determined as fol- Distance O to CR = 1930 yards Distance O to mask = 1030 yards VI (drop) O to CR = 64 feet (447–383) Therefore, the line of sight drops 64 feet in 1930 yards. The amount it will have dropped in the 1030 yards to the mask can be determined by the similar triangles method. APPENDIX 107 1930 : 1030 = 64 : x 1930x = 65,920 x = 34 The line of sight will have dropped 34 feet at the mask, and therefore have an elevation of 447 – 34, or 413 feet. If the mask exceeds this elevation it will block the line of sight. c. Visibility will be blocked by 19 feet of mask because 402 feet of mask plus 30 feet of trees will be higher than the line of sight (413 feet) by 19 feet. d. 53 feet of defilade, determined as follows: Distance O to stream = 1650 yards Distance O to mask = 1030 yards VI (drop) O to mask = 45 feet (447 – 402) Since the line of sight will have dropped 45 feet in the 1030 yards to the mask, the amount it will have dropped when it reaches the stream can be determined by the similar triangles method, as follows: 1650 : 1030 — X : 45 x = 72 feet The line of sight, having dropped 72 feet, will have an elevation of 375 feet (447 – 72). The stream has a known elevation (from the contours) of 322 feet and is therefore 53 feet below the line of vision. 6. a. A correct profile will verify all the answers to 5 above. b. There are three defiladed areas, as follows: (1) From (1898-1835) to (1927-1854). (2) From (1949-1868) to (1959-1875) (3) From (1962-1877) to (2028-19.17). c. On the 360 contour at (1909-1843). 89. Answers To Questions and Exercises, Chapter VIII. 1. a. A vertical is a photograph taken with the camera pointing straight down. b. An oblique is a photograph taken with the camera pointing sideways. 2. The size of the standard single-lens print is 7 x 9 inches. 3. The legend is the technical data regarding the photograph annotated and shown on the lower left edge thereof. 4. The standard legend contains the following data: Type and serial number of the print. The (technical) location. The unit that took the picture. The date and time of day. The focal-length of camera used. The altitude, 108 MAP AND AERIAL PHOTO READING And sometimes the map coordinates and/or the name of the central feature. 5. a. Concrete roads, double track. Identified by its very straight trace, uni- form width, and clear-cut edges. b. A dirt road, unimproved, identified by its irregular edges and narrow- Il CSS. c. An unimproved dirt road, identified by its narrowness and its irregular traCC. d. An improved gravel road, identified by its uniformly broad course and Sweeping curves. e. A small, wooded drainage line. f. A larger, heavily wooded stream line. t g. A cut on the uphill side of a narrow-gauge railroad line. A. A skeet range. i. A railroad train (narrow-gauge) on its track. Note the narrow dark trace of the railroad track. 6. a. Heavily wooded valley or stream bottom, affording good cover and concealment. b. Thin, scattered woods affording little cover or concealment. c. Open grass land. d. Barren area with exposed earth and little vegetation. Characteristic of rugged, eroded terrain. e. Short grass, kept mowed (polo field). f. A golf course, grassed fairways separated by lines of trees. g. Cultivated garden plots. 7. The relative scales of the photo plates are as follows: Plates IV and XI are of about 1:14,000, and similar to Plate II. Plates VIII, IX, and X belong to the same mosaic series as Plate I, and are of a scale of 1:22,000. 8. º “(825–11,500)” 8.25 inches : 11,500 feet 8.25 inches : 138,000 inches 1 inch : 16,727 inches 1 : 16,700 (RF) 9. a. The scale of the map is given as 1:20,000, and the map distance is 5.6 inches. Since 1 inch on the map equals 20,000 inches on the ground, then 5.6 inches on the map must equal 112,000 inches on the ground. The same distance on the photograph measures 5.0 inches. Therefore: APPENDIX 109 5.0 inches (on photo) = 112,000 inches (on ground) 1 inch (on photo) = 22,400 inches (on ground) 1 : 22,400 (RF) b. 1 inch = 22,400 inches (on ground) 1 inch = 622 yards (on ground) (or) 1 inch = 600 yards (approximate). 10. a. The ground distance is 2.6 miles or 164,736 inches. The same distance measured along the road on the photograph is 7.39 inches. On photo On map 7.39 inches = 164,736 inches 1 inch = 22,292 inches 1 : 22,300 (RF) b. 1:22,300 = x : 36,000 22,300 x = 36,000 x = 1.61 inches. The length of a 1000-yard division of a reading scale would be 1.61 inches. 11. a. 306°. b. The location of the patrol was at the small cultivated patch (white spot) at (5.55-C.63), determined as follows: A line was drawn from the road junction at (3.86-E.12) to the center of the school at (0.83-D.65), and its azimuth, based on the known datum line, determined to be 279°. Since the school lay on an azimuth of 300° from the patrol, it follows that the patrol must have been on an azimuth of 120° (back azimuth) from the school. The protractor is placed on the school and oriented on the line constructed above with a reading of 99° (back azimuth of the entering line). An azimuth of 120° is now plotted extending across the photo from the center of the schoolhouse. Twenty-nine hundred yards at 600 yards to the inch is 4.83 inches, and this distance is measured off along the line. 12. Plate I shows a new road along the west slope of Maxey Ridge, generally parallel to the ridge road. It shows that this road continues through the anti- aircraft range area, around the 4th Infantry Woods, and connects up with the dead-end road from Maxey Ridge to Singleton Hill, and continues as the same type of road along what is shown as a trail on Riley Ridge until it joins the First Division Road. 13. The map shows a continuous woods mass from the 30th Infantry Woods to the 7th Infantry Woods, inclusive, some 1300 yards long and 600-700 yards deep. The photograph shows that these woods no longer exist except for one small rectangular clump about 300 yards by 150 yards, located at about (18.8- 19.2) on the map. 14. The map shows a considerable wooded area on the north and east of 110 MAP AND AERIAL PHOTO READING Davidson Hill. The photograph shows that these woods no longer exist except for a small clump in the vicinity of the letters “DAV” in Davidson. 15. Relief of an area is often disclosed by the following: a. Shadow values of ridges. b. Terracing or contour farming. c. Relative lengths of shadows of buildings and trees. d. Bends in unimproved roads. e. The drainage system. 16. The drainage system is the most valuable in disclosing the basic terrain Structure. 17. A stereoscope is an optical instrument for use with photographs that assists in combining the images of two pictures taken from different angles. It is used to produce the effect of depth and therefore to disclose relief detail from photographs. 18. It is necessary to have two separate photographs of the area, taken from the same altitude but from different positions. Ii.il INDEX (Figures refer to pages) Aerial photographs azimuths on, 70 composite, 58 data on, 60 identification of features on, 64 importance of, 56 oblique, 58 orientation of, 61 relief shown by, 74 scales of, 66 stereoscopic study, 77 types of, 57 uses of, 55 o vertical, 57 Answers to questions, 104 Atlas Grid, 63 Azimuth adjustment, grid-magnetic, 28 Azimuth circle, 21 Azimuths on aerial photographs, 70 and direction, 21 measuring map, 21 measuring with a compass, 52 plotting on a map, 24. Back-azimuth, 24 Bearings, direction by, IoI Card, coordinate, 13 Card, photo coordinate, 62 Care of maps, Io.4 Circle, azimuth, 21 Classification of military maps, 98 Compass description of, 49 marching by compass, 53 measuring azimuth with, 52 Composite photograph, 58 Contouring, logical, 99 Contour interval, 39 Contours, 37 Conventional signs, 4, 5 Coordinate cards for use with aerial photographs, 62 for use with maps, 13 Coordinates grid, 12 on 5ooo-yd grid maps, 14 polar, Io Data on aerial photographs, 60 Dead space, 46 Declination, 26 Defilade, 45 Depression contour, 37 Description of photo plates, 59 Determining elevation, 42 Direction and azimuth, 21 Direction by bearing, IoI Distance conversion to march time, 19 converting march time to, 19 determination in the field, 49 measurements, 16, 36 Elevation and relief, 37 Exercises, practical, 14, 19, 30, 47, 79 Fraction, representative, 17 Geographic index, 95 Graphic scales for aerial photographs, 66 for maps, 16 Grid coordinates, location by, 12 Grid declination, 27 Grid-magnetic azimuth adjustment, 28 Grid north, 26 Grid square, location by, II Grid system, Io, 98 Ground forms, importance of, 37 Identification of features, aerial photos, 64 Importance of aerial photographs, 56 Importance of map reading, I Index symbol, I O2 Intersection and resection, 25 Interval, contour, 39 Legend on aerial photographs, 60 Lensatic compass, 49 Location by grid coordinates, 12 by grid square, I I by polar coordinates, Io Logical contouring, 99 Magnetic declination, 26 Magnetic north, 26, 70 Map azimuth, measuring a, 2I Map measurer, 17 Map orientation, methods of, 31 Map reading in the field, 49 Maps, classification of military, 98 Marching by compass, 53 Marginal information, 95 Measurements, distance, 16, 36 Measuring azimuth with compass, 52 Military symbols, special, 5 Mil, the, 26 Mosaic, 59 Oblique photographs, 58 Orientation of aerial photographs, 61 of maps, 3 I symbol, 27 Photo coordinate card, 62 Photo maps, 59 Photo plates, description of, 59 Photographs, aerial, 83 Pin points, 59 Plotting azimuth on aerial photos, 71 Position, locating * by inspection, 34 by resection, 36 by single point, 34 Primary scale, 16 Prismatic compass, 49 Profiles, 43 Protractor, 21 Purpose of text, 2 Qualifications of a map reader, 4 Recognition of features on aerial photos, 64 Representative fraction of aerial photographs, 67 of maps, 17 Resection, intersection and, 25 112 INDEX Ridge lining, 103 Scales of aerial photographs, 66 maps, 16 time-distance, IoI words and figure, 19 Shadow, 61 Signs, conventional, 4, 5 Slopes, Ioz Solutions to exercises, Io.4 Special maps, 98 Stereoscopes, 77 Stereoscopic study, 77 Stream lining, Iog Symbols orientation, 27 special military, 5 Terrain feature terms, 49 Terrain features, military, 73 Terrain map, 78 Terrain structure, 42 Time, distance and, I6 Tone of the image, 63 Topographical features on aerial photos, 64 True north, 26 Uses of aerial photographs, 55 Vertical photograph, 57 Visibility, 45 Words and figure scales, 19 THE MILITARY SERVICE PUBLISHING CO. 100 TELEGRAPH BUILDING HARRISBURG, PA. 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