This looks like a very good solution which economizes flying cost. We must realize 
however, that what is economized is no more than 33% of the cost of the flight necessary 
for the small scale photography. However, the disadvantages of this system are obvious. 
Since we use the same flying height, the precision of the determination of heights and of 
contour lines is the same for the scale 1: 70,000 as for the scale 1 : 21,000. The larger 
scale of photography is compensated by the smaller base height ratio. As soon as height 
measurements must be carried out for forest inventory, the large-scale photographs will 
hardly be better than the small-scale photographs. During a soil survey experience was 
gained with such a case, where photographs 1 : 50,000 taken with a 6” wide-angle camera 
and photographs of transverse oblique cameras 12” covering the same strip, were avail- 
able. The photo-interpretor found that all features depending on the distinction of dif- 
ferences in height, were not better in the photographs 1 : 25,000 than in those in 1 : 50,000 
from the wide-angle camera. Considering the base height ratio this is obvious. 
Because of these considerations we believe that for a systematic planning of air 
survey it would be a better solution to make two separate flights, for which we propose: 
a. super wide-angle, scale 1 : 70,000 — 1 : 100,000, longitudinal overlap 80%, lateral over- 
lap between 20-30% according to the topography. Flying height 6000-8000 m. 
b. wide-angle photography 6”, 9” X 9”, scale 1 : 20,000, flying height 3,000 m. Overlaps 
60% and 20%. 
The large scale photography has in this case the best possible qualities for forest 
inventory and further forest mapping, soil survey and the production of maps for engi- 
neering purposes. 
In case a thorough and precise photogrammetric exploitation of the photographs 
1:20,000 is carried out for other purposes and an aerial triangulation of these photo- 
graphs is necessary for large scale maps, it is evident that for this area no triangulation 
of the small scale photographs is necessary. Then the map 1 : 100,000, produced without 
aerial triangulation as mentioned above, will be sufficient as a base map for the inter- 
pretation, in particular for the soil surveyor. There remains, however, the problem how 
to transfer the results of the photo-analysis to the map 1 : 100,000. 
Since soil surveys are mainly carried out in flat or softly rolling terrain, relief 
displacement will never cause great difficulties. Only in those cases in which it is too 
difficult to identify points from the photographs in a map, could it be desirable to apply 
to the soil survey the same procedure as proposed here after for forest mapping. 
Forest mapping will in general require a more complicated photogrammetric proce- 
dure. This applies either to cases in which maps in the scale 1: 20,000 and even larger 
are desired, or to cases where high mountains cause unacceptable relief displacements 
and influences of model deformations. In such a forest map, however, the linear preci- 
sion needs in general not to be very high. 
The procedure we propose for those areas where no precision maps and only forest 
maps from the photographs 1:20,000 must be derived would be to choose on the photo- 
graphs 1: 20,000 a complete set of control points which will be transferred, by means of 
a limping stereoscope, to the photographs 1 : 70,000. 
f. Determination of control points. 
These points are determined in three coordinates by means of aerial triangulation 
of the last photographs. To this we can apply the digital aerial triangulation using a 
stereo-comparator and high speed computers, not so much because of precision, but 
because of the greater economy. 
Nevertheless, it is important to indicate the precision, which can be obtained by 
means of such a procedure, as this precision will be decisive for the use we can make 
without any further ground survey of the photographs 1 : 20,000 for the production of 
topographic maps.