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98 REPORT OF COMMISSION VII 
LIMITATIONS, ADVANTAGES AND DISADVANTAGES OF PHOTOGRAPHIC 
INTERPRETATION. 
Photo interpretation may be systematic, direct or comparative. It is system- 
atic when the photo interpreter has no information at all on the area under 
examination and he examines the photos following a rational and scientific 
method; it is direct when the photos are employed for control to verify or deny 
the validity of information coming from other sources; and it is comparative 
when the study of photographs is done by comparison with other photographs 
taken at earlier dates. It is clear that all three forms of photo interpretation are 
useful and that they frequently complement each other. 
About the exactness of the information derivable from aerial photographs 
we can say that the per cent error in identification of a given detail or entity 
depends primarily upon the type of detail itself (its form, dimensions, camou- 
flage, etc.) and upon the experience of the photo interpreter. 
Photo interpretation offers the special advantage of supplying a synthetic 
picture of a very large zone and thereby offers the possibility of obtaining in a 
very short time a complexity of information or data relative to that zone. This 
information usually can be obtained by non-photographic means only with great 
difficulty, if at all, and requires much time. As to the information of the ter- 
rain, with reference to morphological characteristics, nature of the soil, works 
of man, etc., aerial photography offers the greatest of possibilities with a mini- 
mum of error. With regard to such man-made works as dwellings, roads, rail- 
roads, waterways, etc. aerial photos give a complexity of information not avail- 
able on the most up-to-date topographic maps. They allow an accurate study 
of the last-accomplished works, the destruction and damage due to air or ground 
attack, etc. 
Finally, aerial photographs offer the great advantage of supplying an 
"alive" picture of human activities at the moment of greatest interest, while 
topographic maps give only “static” vision. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
    
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