WWI Trench Maps & Aerial Photographs
How to Read Aerial Photograph Numbers:
There can typically be 3 or 4 lines of numbers present on WWI air photos.
These numbers usually appear in the upper, right-hand corner of the photo but placement can vary. These lines are normally in the same sequence as listed below but have also been known to vary.
The First line indicates the film negative series and the photo number.
An "O" was included preceding the photo number if the photo was taken at an "oblique" angle rather than the normal vertical angle. Scale remains constant over the entire photo in vertical angle shots but varies from one side of a photo to the other in oblique angle shots.
The Second line indicates the day, month, year and time of day when the picture was taken.
The Third line lists map reference numbers that correspond to the area covered by the photograph (see: How to Read Map Reference Numbers).
A letter and number combination (e.g. F=8 or F-8) can be found on the second line following the date information or occasionally on a separate, fourth line as in the example below. It indicates the focal length of the camera in inches and can be used to determine the scale of a photo if the altitude is known.

Note: The symbol that looks like a white cross to the left of the numbers in the closeup is actually a North arrow.

numbering on a typical air photo
Here is an example taken from the photo above:
F- 8.

Line 1: 4B2205.
This line is a combination of the film negative series number & photo number:

4B (negative series number) 2205 (photo number).

Line 2: 17.7.18-1.

17. (day), 7. (month), 1918. (year) -1. (time of day).

Line 3: 27.X21.

27. (map sheet number)

X21.22.27.28. (squares X21, 22, 27 & 28 on map sheet 27)

36a. (map sheet number)

F4. (square F4 on map sheet 36a)

The area covered by this air photo is the equivalent of the area covered by squares X21, X22, X27 and X28 on map sheet 27 and square F4 on map sheet 36a.

Note: the periods should help you determine where the map sheet numbers end and where the numbers for the squares begin. Map sheet numbers can also contain letters (e.g. "36a") as in the example above.

Line 4: F-8

(focal length of camera = 8". this can be used in conjunction with the altitude, if known, to determine the scale of the photo).

Formula for calculating scale using focal length and altitude

German Notation:
The following is an approximate translation of an example of the notation sometimes found on the verso (back) of German aerial photographs:
German English approximate translation
Feld-Flieger Abt.__ Field-Flight Dept.__
Bild no.__ Photo No.__
objekt__ object__
Aufgen. durch__ Photo taken by__
Vermessungs Abetilung nr.__ der __ Armee Surveying Department No.__ of the __ Army
Briefstempel__ Letter Stamp__
Kartenstelle Hy__ Map Dept. Hy__

Diagram of Overlapping Photo Technique:
Diagram of aircraft taking overlapping air photos

Contact: mapref@mcmaster.ca