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The most important of these services is without any doubt the Soil Survey 
Institute, which, under the direction of Prof. Dr. C. H. Edelman, has made 
it its task to compile maps showing the details of the soil. Experience has 
taught us that a proper combination of field work and photo-interpretation 
speeds up production and makes the results more reliable. The Soil Survey 
Institute prefers vertical photographs on a scale of between 1 : 7,500 and 
1 : 10,000. Photographs up to the scale of 1 : 20,000 are less useful, while 
still smaller scales are to be qualified as of no use whatsoever. So far this 
Service has not carried out any experiments with special filters and colour 
photography. 
The Topographical Service at Delft has found photo-interpretation to be 
indispensable for map-making. Reconnaissance activities in the field can hardly 
be replaced by interpretation in the office. As mentioned before, photo-inter- 
pretation has become known in the Netherlands mainly through this Service. 
Interpretation for geographical, hydrological, archeological and many other 
purposes is practised, elaborated and propagated by the Topographical Service. 
The Agricultural Planning Service at Utrecht prepares the projects for 
the re-allotment of certain agricultural areas. After compiling a map on a 
scale of 1 : 5,000 from copies of cadastral plans, these maps are completed by 
means of ground surveys and interpretation of air photographs. The procedure 
of re-allotment ‘has been indicated in Chapter IV. The photographs are a 
great help when evaluating existing lots. 
The Government Forest Service uses air photographs for making forest 
maps and for forest statistics. The purpose of their interpretation, which is 
carried out both with and without a stereoscope, is to trace wood stands, road 
plantations and uncultivated grounds. The exact situation of the borders be- 
tween the various parcels is determined from the photographs. The different 
kinds of wood in each parcel are read from the same photograph. After this 
interpretation a field check is necessary. This Service prefers vertical photo- 
graphs on a scale of 1:10,000 taken during the leafless period.