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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
Soil investigations to be carried out in this phase of development planning 
are the most difficult of all types of soil surveys. Predictions for agricultural 
potentialities of rather large areas have to be given, with the aid of only a 
limited number of field observations and laboratory analyses, while all factors 
concerned have to be taken into account. Very often no crops on which pre 
dictions can be based are grown in those regions, or only a primitive small 
scale agriculture exists. Much depends on the results of the surveys in this 
stage and the person who carries out the aerial photo interpretation and the 
field work bears a great responsibility. It is therefore of great importance that 
investigations on soil and land potentials in development projects in this phase 
are made by highly qualified soil and land classification experts. Not all soil 
experts, who may be extremely qualified for detailed soil studies, are able to 
carry out this type of soil investigation, which requires the ability of generaliza 
tion. 
Besides the investigations for soil survey and land classification, there should 
also be general studies on geology, hydrology, and climatology. The results of 
all these studies have to be incorporated in one report, leading to a number of 
recommendations. 
Soil investigations in the third phase 
In this phase of the preparation of a development project more specialists 
(agriculture, engineering, irrigation, drainage, economy etc.) have to join the 
team. The main purpose is to make a development plan (avant project), which 
is detailed enough to inform the Government on some alternative plans of 
development; their costs, inputs, outputs, farm economy, marketing etc. 
Compared with the first and second phase, the third phase of planning will 
take much more time and many more specialists have to co-operate, in order 
to provide a realistic development plan. It is not necessary that all details are 
worked out (e.g. details such as structures, canals, ditches, drains, inlets, outlets, 
farm boundaries, farmhouses, new villages etc), because this detailed work 
takes very much time. This is only done when the project is prepared for 
tendering. The idea of phase 3 is to prepare everything in such a way, that the 
responsible authorities obtain a good idea of what can be done successfully; 
how many farms can be established, what can be grown, what may be expected, 
and what will be the financial consequences etc. 
As far as soil survey and land classification is concerned a semi-detailed soil 
survey will be neccessary. Such a survey, as well as additional land classification 
surveys, can easily be made by a study of soil conditions in the field, in combi 
nation with aerial photo interpretation. The well-known methods and proce 
dures developed in the I.T.C. and applied in quite a number of countries (see 
I.T.G. Publications, series B, 2) and described in the Manual of Photographic 
Interpretation already mentioned, can be applied. The application of aerial 
photographs in this type of semi-detailed soil surveys has many advantages 
and it would be a waste of time, money and manpower, to undertake such a