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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
cannot be collected by aerial photo interpretation. A real soil survey in the 
field has to be made in those sections of the project area where special infor 
mation on soils is needed. The role of aerial photo interpretation can often be 
neglected. 
Conclusions 
Investigations concerning planning and execution of agricultural develop 
ment of a country are carried out in a number of phases which have a general 
application. It begins with very general work in large areas, and it ends with 
quite detailed investigations in certain sections of a project. The general survey 
executed at the beginning, and covering the whole country, or at least a great 
part of it, could never be done in an efficient and effective way if no aerial 
photographs were available and if no proper techniques of aerial photo inter 
pretation had been developed. Soil surveys, which should provide the nec 
essary basic data, would be almost impossible for large project areas, without 
applying aerial photo interpretation. The costs would be too high, there would 
be a great shortage of experts and work would take too much time. We there 
fore conclude, that aerial photographs are not only a very helpful and econ 
omic tool in the planning and preparing of development projects, but we can 
even state that it would be impossible to execute this type of work if no aerial 
photos and mosaics were available. The most economic use of aerial photo 
graphs can be made during the first two phases of planning, whereas their most 
effective use for soil survey purposes is made during the third phase. 
In nearly all countries where development programmes are made, aerial 
photos and mosaics are available at the present time. However, many specialists, 
who make use of these photographs, often use them in a rather simple way. 
Much more could be done if they knew and could apply the various tech 
niques of aerial photo interpretation. 
Discussion 
Mr. N. Leneuf (France) remarked that, in areas covered by a dense tropical forest, detailed 
field investigations in pilot areas are absolutely necessary. Dr. Buringh agreed with this. 
Mr. Retzer (U.S.A.) agreed with the steps outlined by the speaker and added that it is impor 
tant to realize that the required soil information cannot be determined from the stereoscope 
alone. No information about texture, pH, drainage, etc., can be obtained from photographs. 
Asked by Mr. Latarche (France) to indicate more precisely the dangers of misinterpretation 
incurred in phase 3, Dr. Buringh answered that the soils as such are not shown on the aerial 
photographs. Interpretation is guesswork, whereas soil survey quite definitely is not.