How to Read Aerial Photograph Numbers:
There can typically be 3 or 4 lines of numbers present on WWI aerial photographs.
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 can indicate either the negative series and photo number or, alternately, can indicate the squadron number followed by the series/camera type and photo number. Occasionally an "O" was included preceding the photo number if it was an "oblique" rather than a vertical angle shot.
- 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.
Here is an example taken from the photo above:
4B2205.
17.7.18-1.
27.X21.22.27.28.36a.F4
F-
8.
Line 1: 4B2205.
The entire line can simply pertain to the negative series number and photo number:
4B (negative series number) 2205 (photo number)
Alternately,
it can refer to the squadron number, series/camera type, and photo number but these would usually be separated by periods:
4. (squadron number), B. (negative series/camera type), 2205. (photo number).
Line 2: 17.7.18-1.
17. (day), 7. (month), 1918. (year) -1. (time of day).
Line 3: 27.X21.22.27.28.36a.F4.
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).
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