1. The Rivermap on scale 1:10 000, in aid of the up keep and admi- 
nistration of the rivers. These maps are made by aerotriangulation (Wild 
A 5 or radial triangulator). 
Average number of ground control points: 1%-2 per 5 photographs. 
The methods for the construction of the river maps are described in the 
National Report of 1938: 300 km? have been plotted since 1948. 
2. Technical maps on scale 1:2500 and 1:5000 of river- and creek- 
areas. This kind of maps is on behalf of technical projects. The photoscale 
is resp. 1-7500 and 1:10 000. After aerotriangulation with 1%-2 ground 
control points per 5 photographs the areas are plotted by means of the 
«Wild A 5» and the Zeiss-Stereoplanigraph. 
For the map 1:2500 and a photoscale 1:20 000 only ground control 
points have been used. 120 km? have been plotted since 1948. 
3. Road-maps on scale 1:1000. Photographs on scale 1:5000. Only 
ground control points (4 per pair of stereoscopic pictures). Plotted in ste- 
reoplanigraph. 
4. À map on scale 1:10 000 on behalf of an extensive dam-lake project 
in Surinam. 
The photoscale is 1:40 000 (Wild R. C. 5 camera f = 11,5 em) Geo- 
detic data: Astronomical stations and several bases. The altitude data 
have been obtained by barometric measurements along the rivers. 
The aerotriangulation was executed by means of the Wild A 5 in- 
strument and the plotting by {Wild A 6 apparatus. 2660 km? were 
plotted till Dec. 1951. 
Ground control measurement are no yet available. All these activi- 
ties are executed by the Royal Dutch Airlines. 
b) Maps for-Region and Town planning. 
1. Maps for town planning on a scale 1:1000. Cameratype: Wild 
R.C. 5 Aviotar f — 21 em photoscale 1:5000 to 1:8000. Only ground con- 
trol points have been used. 
A surface of about 12 km? has been plotted till Dec. 1951 (Wild 
A 5) The mean error is about 15 cm in position. 
2. A map on scale 1:10 000 on behalf of the drainage of a large Dutch 
area (surface 600 km?). 
Photoscale 1:20 000. Aerotriangulation in Wild A 5 (114-2 ground 
control points per 5 photographs). After rectifying the plotting was exe- 
cuted by means of a tracing stereoscope. 
3. Dune maps on scale 1:1000, plotted, in stereoplanigraph on be- 
half of the provincial waterworks. 
Photoscale; 1:5000. 
Only ground control points have been used. 
The equidistance of the contour lines is 1 and 2 m. 
— 85