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Transactions of the Symposium on Photo Interpretation

working on such development projects are always: how to carry out such in
vestigations and how to evaluate the results. Other questions are: the type
and technique of soil survey to be applied under the specific conditions in a
project, and the most suitable procedure to be followed in aerial photo
In this paper we shall try to give a general scheme for the use of aerial
photographs in the soil surveys of development projects. It should, however,
be understood that in each particular case this scheme has to be adapted to
the prevailing economic and environmental conditions and to the purpose of
the project.
Phases in development projects
In many countries Governments wish to start on a particular project, which
has to be finished as soon as possible. It is often more useful, first of all, to
investigate the whole country, or at least a large part of it. Such an overall
study, which can be carried out in a relatively short time and at low costs,
shows the potential agricultural regions, which seem to be promising for
Taking into consideration the various factors concerned, one of these
regions may be selected as a development project. Various types of investiga
tion have to be carried out in this project area, firstly on a rather general
basis and later in somewhat more detail.
The next step will be an “avant project”, a rather detailed study as a basis
for a plan of development, a plan of operations, and a rough calculation of
costs, outputs and inputs.
The final step is the execution of the project. Here too, many, often quite
detailed, studies have to be made for specific purposes.
The four steps or phases mentioned above are:
1st phase: an overall study of the country, indicating the potential agricul
tural regions,
2nd phase: general investigations in a project area,
3rd phase: investigations for an “avant project”,
4th phase: detailed investigation for the execution of the project.
The investigations to be made during these four phases, have quite different
characters, this is especially the case for soil survey and consequently also for
aerial photo interpretation. Methods and techniques of soil survey and aerial
photo interpretation have to be adapted to the type of investigation to be
carried out in each phase, to the physical conditions of the terrain, and to the
purpose for which the project has to be made.
Soil investigations in the first phase
During the first phase the purpose of the investigations is to select the poten
tial agricultural regions, which seem promising from the point of view of