Air Fronts: FM 21-26 - Advanced Map and Aerial Photograph Reading

Air Fronts: FM 21-26, Advanced Map and Aerial Photograph Reading

FM 21-26, Advanced Map and Aerial Photograph Reading, War Department Field Manual, Washington, 23 December 1944

(This manual supersedes FM 21 - 26, 17 September 1941, including C1, 15 May 1942, TB 21 - 25 - 12 March 1944; TB 21 - 26 - 1, 23 February 1944; and Training Circular No. 66, War Department, 1944.)

Table of Contents

Sections		Paragraph
SECTION I.	INTRODUCTION.
	Purpose	1
	Scope of Training	2
SECTION II.	MAPS
	Definition	3
	Classification	4
	Care in the Field	5
SECTION IlI.	CONVENTIONAL SIGNS AND MILITARY SYMBOLS.
	Conventional Signs	6
	Military Symbols	7
SECTION IV.	MAP MEASUREMENTS
	Scale	8
	Measuring Devices	9
	Conversion Factors	10
	Determination of Map Scale	11
	To Construct a Graphic Scale	12
	Time and Distance	13
	Time-distance Scales	14
SECTION V.	DIRECTION AND AZIMUTH.
	General	15
	Units of Angular Measurement	16
	Base Direction	17
	Declination	18
	Declination Diagrams	19
	Azimuth	20
	Bearing	21
	Protractor	22
	To Measure Azimuth of Any Line on a Map	23
	To Plot an Azimuth on a Map	24
	Compasses	25
	Traverse	26
SECTION VI.	GRIDS AND COORDINATES.
	Military Grid	27
	Coordinate Scale	28
	Using Engineer Scale	29
	Polar Coordinates	30
	Rectangular Coordinates	31
	Thrust Line	32
	Map Templates M1 and M2	33
	Geographic Coordinates	34
	Geographic Coordinates on Foreign Maps.	35
	U. S. Domestic Grid System	36
	World Polyconic Grid	37
	British Grid System	38
	Air Defense Grid	39
	Fire-control Grid	40
	Point-Designation Grid	41
SECTION VII.	ELEVATION AND RELIEF.
	General	42
	Contours	43
	Hachures	44
	Layer-Tint System	45
	Ridge and Stream Lines	46
	Slopes	47
	Profile	48
	Visibility	49
SECTION VIII.	ORIENTATION.
	General	50
	Expedient Methods of Determining True North	51
	Location of Distant Point by Intersection. .	52
	Resection	53
SECTION IX.	AERIAL PHOTOGRAPHS.
	General	54
	Types	55
	Pin Points	56
	Strips	57
	Mosaics	58
	Marginal Data	59
	Fiducial Marks	60
	Source of Error	61
SECTION X.	AERIAL PHOTOGRAPHS AS MAP SUBSTITUTES.
	Comparison of Aerial Photographs with Line Maps	62
	Identification	63
	Scales	64
	Graphic Scale	65
	Distance	66
	Direction	67
	Orientation	68
	Point-designation Grid	69
	Emphasizing and Clarifying Detail	70
	To Index and Plot Aerial Photographs	71
SECTION XI	PHOTOMAPS.
	Types of Photomaps	72
	Marginal Data	73
	Military Grid	74
SECTION XII.	STEREOVISION.
	General	75
	Learning to Use a Stereoscope	76
	Stereoscopes	77
	Study of Stereo-pairs	78
	The Floating Line	79
APPENDIX	PROJECTIONS

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