REPORT OF COMMISSION VII 
GVII-59 
difficult to apply in air photo interpretation, but which is one of the more valu 
able techniques to prevent assumptions. 
4) The photography should be analyzed for its photographic qualities alone. 
Most commercial photography taken in peace time is of high quality. Occasion 
ally, however, there are variations in photographic characteristics which are 
purposeful or accidental and which cause minor problems in interpretation. 
When interpreting military photography, major problems may arise because the 
photographing, development, and printing often are done under trying and im 
perfect conditions, particularly those of combat. Clouds may hinder observation 
of the ground; static streaks or scratches may simulate the works of man, spots 
from drops of fluid may be distracting; objects may be slightly blurred; or scales 
may vary. Nevertheless, this type of photography is available for large parts of 
the world and should be used whenever at all possible. 3 
Topical Procedures 
Application of the general procedures to the topical is seen in the suggested 
order of interpretation of topics. This is: transportation, drainage, surface 
configuration, vegetation, agriculture, rural non-agriculture, and urban features. 
Specialized topics, such as military features, should be added at the end. Such 
an order is effective because it leads an interpreter methodically and, usually, 
from the better known to the less well known, as well as from the general to the 
more specific features. 
Most persons feel generally familiar with land transportation. Thus, begin 
ning with such things as are recognizable from every-day experience, immedi 
ately builds confidence. In addition, features are located which are basic to 
most research. Also, because transport lines are usually functions of the places 
they connect, an interpreter is prompted to begin with small-scale photos so 
as to see in one view the places connected and the connecting links. Then, it is 
logical to proceed to drainage which is often confused with transportation be 
cause both features commonly are linear, close together (as in a valley), and 
similar in size and photographic tone. 4 
Determination of the drainage pattern is fundamental for interpretation 
of surface configuration which may logically follow. An understanding of both 
drainage and surface configuration is needed for the interpretation of vegeta 
tion; and because all three topics usually have wide-area patterns of distribu 
tion, an interpreter is led by this order to begin with the smallest scale photos 
available. 
Crops are logically next because they are similar photographically to natural 
vegetation, and they and other agricultural uses of land often are distributed 
in close relationship to the topics previously noted. This leaves the non-agri- 
cultural rural uses of the land, several of which are like the intensive land uses 
found in cities. This increased intensity of use introduces a need for larger scale 
3 Stone, K. H., World Air Photo Coverage, 1953, Photogrammetric Engineering, v. XX, 
1954, p. 605-610. 
4 The significance of photographic tone in interpretation probably has been overemphasized. 
Tone is the result of the reflective properties of an object, not necessarily its color. And the re 
flective property is dependent upon the position of the object with respect to the sun as well as its 
density. Bodies of water, for example, may have all the tonal values from white to black on a single 
photo, because of changes of the angle of reflection of sunlight to the camera, of shallowness of the 
water, or of motion of the water, or of the amount of sediment in the water. Further, the tonal 
values are relative to each other rather than constant for an object, because the tones are partially 
a result of the exposure, development, and resolution of the film, as well as the proximity on the 
ground of objects and, therefore, the scale of the photography.