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faster than would have been possible without those keys. But from a scientific 
point of view there is a great danger. Many people knowing almost nothing of 
photo-interpretation will take a photograph, observe an object on it and iden- 
tify it with page so and so, number so and so of an interpretation key. 
That is an evil, for we know too well how the aspect or appearance of any 
given object may change depending upon its natural circumstances. 
The use of a photo-interpretation key as a sort of a dictionary is not jus- 
tified; however, that is what people will do. A dictionary of a good quality can 
be of great value. However, if one who does not understand a language very 
well tries to write a leter in that language with the aid of the dictionary he 
will write complete nonsense. 
Exactly the same thing holds for photo interpretation and interpretation 
keys. 
There are too many people who have merely seen a few aerial photo- 
graphs and call themselves already interpreters. We meet them almost daily. 
For such persons the interpretation keys are dangerous. These keys should be 
highly restricted and though articles illustrated with key data are very interest- 
ing and convincing I believe that the publication may lead some people astray. 
If I must admit that I have studied and interpreted some 600,000 aerial 
photographs and that nowadays my knowledge of photo-interpretation is still 
limited then either you might consider me a person deprived of any intelligence 
or you might take photo-interpretation to be an extremely difficult science. 
To make myself a compliment I believe the latter is true. Well, I think I have 
said enough about that subject and now you may be anxious to hear what is 
my technique of photo-interpretation. 
First, I would like to ask a question. Is there anybody who can show me 
an interpretation key for detectives showing that finding a cigarette stub in 
combination with a hair, a piece of thread and a footprint in a given position 
indicates that a murder has happened on Connecticut Avenue, number X, the 
murderer being a man of 61, crippled on his right side, even as Conan Doyle 
makes Sherlock Holmes find his solutions? That interpretation key does not 
exist, I am sure. 
So I have no key either. The differences in soil type; the differences in 
reaction of water and vegetation upon that soil type; the changes in shade of 
that soil type in connection with season, rain, dryness, frost, and so much 
more; the erosion of previous forms of that soil by water, air and wind; the 
forms of sedimentation; — they all make it almost impossible to set up rules. 
Furthermore, forms become more and more erroneous since nature has 
mixed and changed these forms during hundreds and thousands of centuries, 
as a result of which reduction of the facts is still more impossible. 
It is therefore that I see the only possibility of real photo-interpretation 
lies in clearly mapping all initial interpretation data, photograph by photo- 
graph. Such a process will show us the facts on a larger base and thus make 
more comprehensible what happened in the past. 
But then the photo interpreter has to find his own way, his own techni- 
que. So I follow my own perception and that is my technique. In my opinion 
it is only in this way that a photo interpreter will obtain the unbelievable 
results which the aerial photographs make possible. Only in this way will one 
be able to make a study like I did of my country. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
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