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REPORT OF COMMISSION VII 85 
B) INTERPRETATION OF AIR PHOTOGRAPHS IN COMBINATION WITH PHOTOGRAM- 
METRICAL SURVEYING: 
Any given groundpoints or groundlines which are to be plotted may be 
entered into the air photographs either in reconnoitring or else, and partly, by 
mere interpretation. Thus the interpretation of air photographs was first used 
in Switzerland for purposes of the consolidation and fusion of landed property 
in 1947. In the taking of air photographs of the old landed property of a 
community in the scale of 1: 1,000 the results of the valuation were entered 
into the air photograph and the new lines of demarcation thus obtained were 
plotted at the stereocartograph together with the boundaries of the old property. 
Such or similar combinations of Photo interpretation followed by photogram- 
metrical plotting have proved useful in the Swiss Survey of Landed Property 
as well as for other elements contained in cadastral plans for years. 
For geological surveying the procedure was first carried out and recom- 
mended by Dr. b.c. Robert Helbling in 1938. Boundaries of rock layers and 
other geological details were first entered into the air photographs and then 
evaluated with the topographic data of the pictures. Thereby a perfect combi- 
nation of the topographic and geological map contents was assured. However, 
the procedure evidently seems to be economic only for areas for which there is 
no corresponding and modern topographic map available, i.e. where the photo- 
grammetric photograph has to furnish both the topographic and geological data. 
The trial photographs by Helbling covered large parts of the alpine area of the 
Canton of Glarus and led to some essential corrections of the official geological 
map of the said Canton. 
c) THE PHOTOGRAPHIC MATERIAL AVAILABLE: 
From what has been said above it is evident that air photographs are seldom 
taken in Switzerland for the single purpose of interpretation alone. Only the 
map-making organisations of the state, such as the Federal Office of Land Topo- 
graphy and the Federal Survey of Landed Property (Cadastral Survey) have 
survey aeroplanes, cameras for air photogrammetry and the necessary staff at 
their disposal. With the exception of occasional photographs taken by the Swiss 
Air Mail Company, “Swiss Air”, most vertical photographs are taken primarily 
for surveying purposes, such as the drawing of new official maps and their 
supplementing and also of the planworks of the Landed Property Survey. The 
resulting material can then be put at the disposal of others interested for pur- 
poses of interpretation etc. Also where special air photographs are necessary as 
e.g. for the research of avalanches, these are made available by the aforemen- 
tioned public offices. Separate organisations for occasional purposes of inter- 
pretation would not be economic in Switzerland. 
It follows therefrom that nearly all air photographs, also those taken for 
purposes of interpretation, are governed by the requirements of the topographic 
survey. As these photos overlap each other they make stereoscopic observation 
possible. 
We have at our disposal in Switzerland to-day: 
1) Photographs taken with the Wild Camera RC 5 (for films 18 X 18 cm) or 
RC 7 (for plates 15 X 15 cm) flight altitude about 4000 m above ground, 
scales of pictures about 1 : 15.000 up to 1 : 20.000. Surface photographed