by means of the Zeiss-Stereoplanigraph and the stereoautograph Wild 
A 5. As a rule four ground control points are used throughout the area 
of overlap of a pair of stereoscopic pictures. 
Recently experiments have been made on aerotriangulation for 
mapping of a re-allotment map on scale 1:2500 with photographs on 
scale 1:7000. On an average the number of ground control points amounts 
115-2 per 5 photographs. The results of this mapping are not yet known. 
The production speed with the above-mentioned instruments de- 
pends on the photoscale and map-contents and ranges in consequence 
from 3 to 8 ha/hour. 
For cadastral- and re-allotment purposes the photogrammetry is 
only used for open ground, without woodland of some significance. 
Generally a re-allotment of polder areas begins with a basic plan 
obtained by aerial survey. If the accuracy comes up to the cadastral re- 
quirements, the measurements can practically be limited to new roads 
and watercourses new property-borders and some borders invisible from 
the air. The re-allotment « Beltrum » is an example of no polder area, 
à district of many wood-borders. This re-allotment has not yet been fini- 
shed. The working-method is as follows. The roads and watercourses are 
marked out, measured on the ground and plotted on new maps. The 
photographs on scale 1:7500 are magnified to 1:2500 by making use of 
4 ground control points per photograph. It’s an approximated rectifying. 
The « inside work » of the map is filled up in this framework of roads and 
watercourses by copying the photographs 1:2500. The accuracy of these 
maps 1s sufficient for the project and the computing of the new division 
into lots. It may be expected a few-measurements on the ground will 
only be needed for coming up to the cadastral requirements. So this re- 
allotment Beltrum, whereby large ground-ameliorations have to be done, 
is an example of the classic method concerning the use of aerial photo- 
graphs. 
The magnified photographs on the scale 1:2500 have been used for 
the valuation of the grounds too, so that this could be accelerated consi- 
derably. 
The experience with the use of magnified photographs for the va- 
luation, the inquiries into the rights on the ground and for the view of 
the ground is so favourable, that we use these photographs independent 
of the fact if aerial survey will be executed. 
Generally speaking film negatives often show great deviations cau- 
sed by irregular shrinkage of this material. 
c) No pre-existant maps are put up to date with photogrammetry. 
2) Other maps for various purposes. 
a) Maps for projects of public works. 
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