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undertaken on the basis of conventional techniques, and methods. There 
is an ever-increasing demand for such surveys. The fact that more than 
half of the world's population is undernourished and that, consequently, 
there should be a substantial escalation in agricultural surveys and 
2) 
veys should be adequate and provide a maximum of results with a mini- 
planning, is just one reason. In order to be effective, such sur- 
mum of expenses. Questions to be asked before embarking on & survey 
will, therefcre, be the following: "Has anybody carried out a survey 
in a similar area before ?" ; "Were the techniques and methods used 
adequate and did they give the results needed ?" ; "If a project was 
not entirely successful, would it be possible to inerease survey effi- 
clency and reliability. ^" ete. 
The problem of information exchange is particularly serious in 
photo interpretation, because it is a technique used with essentially 
the same basic principles by many branches of the earth and social 
sciences. Therefore, each branch can possibly learn from the other. 
Articles dealing with the use of photo interpretation are published 
in special journals on photogrammetry and photo interpretation in part 
only; a probably at least equal amount of papers appears to be scatte- 
red over a great variety of geographical, geological, pedological, 
geobotanieal, agricultural, arehaeolosieal,. sociological, eto. jour- 
nals. 
The development of publishing and reporting activities in photo 
interpretation (incl. space photography and remote sensing) is illu- 
sStrated by Figc.l. This diagram is based on the number of entries in 
the library card catalogue of the Department of Geography, University 
of Zurich, which has been building up a specialized; library and docu- 
mentation on photo interpretation during the past 10 years or so. This 
card eatalogue not only contains the documents actually present in the 
departmental library, but further references as well. It goes without 
saying that it is not complete. Also, there may have been a thematical 
bias in the gathering of information. Nevertheless, we believe that 
the figure provides a picture which is representative of the situation 
in general. The number of entries has been counted for 5-year periods, 
and the results are shown in the form of a histogram. We start with a 
figure of 3 for the first period (1911-1915) and end up with a figure 
of 2671 for the last period considered (1961-1965). The smoothed curve 
ig, in principle, based on the histogram but, in addition, tries to