WORKING GROUP 3 
BURINGH 
141 
survey if no recent aerial photographs of good quality and on a scale of 
1 : 20,000 or 1 : 25,000 are available. If, for the first step of development, the 
whole country, or at least quite a large part of it , were covered by an air 
survey 1 : 50,000, then for the second and third phase an aerial survey 1:20,000 
or 1:25,000 would be needed; only for those regions, however, which are 
expected to have good potentialities. 
The application of aerial photo interpretation in soil surveys of develop 
ment project areas often leads to soil maps showing those soil mapping units, 
which can easily be recognized and analysed in the stereoscopic photo-image. 
The study of soils in the field aims at ascertaining the soil characteristics 
corresponding to the characteristics of the photo-image. Very often, however, 
the classification of soil mapping units has also to be based on some other soil 
characteristics, which can only be known if soils are studied and mapped in the 
field. Soil texture is a good example of such a characteristic. As far as soil 
qualities are concerned, soil permeability is an example too. 
Both soil texture and soil permeability are quite important in drainage 
studies. There is still a tendency, in publications on aerial photo interpretation 
in soils, to suggest that soil texture and even soil permeability can be deter 
mined by photo interpretation. Such publications are wrong and I deeply 
regret that even some firms in air survey and aerial photo interpretation con 
tinue to make misleading propaganda. 
Another serious danger of applying aerial photo interpretation in soil sur 
veys, to which attention was also drawn in the Manual (page 665), is that soil 
maps and reports are based on insufficient field and laboratory investigations. 
I have already seen various soil maps prepared in such a way. This problem 
could easily be solved if: 
a. the method of soil survey and the technique of aerial photo interpretation 
were described in detail in the soil survey report, 
b. the results of the detailed field investigations in all sample areas were in 
cluded in the report, 
c. a map, indicating the location of all profile pits and borings was attached 
to the soil map and report. 
Unfortunately these suggestions are followed only in a few soil surveys. 
For most “avant projects”, the semi-detailed soil surveys made by aerial 
photo interpretation in combination with an appropriate quantity of field and 
laboratory investigations give very valuable results. The biggest advantage is 
still, that the most important information on soil conditions can be supplied in 
a relatively short time, after starting the project studies. The result is, that 
having these data available at an early stage of planning, the information on 
soils is intensively used by all the specialists needing them. 
Soil investigations in the fourth phase 
For the detailed planning, preceding the execution and construction of the 
works in a project, much data on soils is needed. For the most part this data