9 NETHERLANDS 
NATIONAL REPORT OF THE TOPOGRAPHIC SURVEY 
A) MAPS ON SCALE 1:25 000 AND MINOR SCALES. 
a-b) The Topographie maps of the Netherlands are principally 
obtained by rectifying single photograms on a scale 1:16 666. Except 
for the South East part of the country, a very small hilly region, the ste- 
reophotogrammetry is used on a scale 1:10 000. For tropical areas con- 
tour maps 1:20 000 and 1:25000 are made by using the Stereoautograph A 
6 of Wild. Some plain tropical areas are rectified on the scale 1:20 000. 
c) The equidistance of the contour lines is 2,5 m for the topogra- 
phic maps and 8, 10 and 20 m for the maps of tropical areas. The scale 
of the photographs is 1:20 000 for the Dutch areas and 1:16 000, 1:20 000, 
1:30 000 and 1:40 000 for the tropios. 
d) In the Netherlands the map is based on the first-, second- and 
third order triangulation and levelling of the country. In the tropics 
the geodeti data consist of astronomical points, triangulation points 
and bases of + 8 km. The distances between the points vary from 40- 
150 km. 
Altitude data: trigonometric-or barometric points. 
e) The accuracy obtained and checked for the Netherlands is; 
1) by the rectifying method: + 2,5 m in position (map scale 1:16 666) 
+ 10 cm in height (data obtained by levelling). 
2) by the method of restitution of couples of stereoscopic plates: 
60-100 cm in height, 100-200 cm in position. 
In the tropics only the height data of the maps are checked by sur- 
veying some traces on the ground. The differences in height do not ex- 
ceed the local variation in tree-height. 
The accuracy of the obtained X- and Y-values has never been con- 
trolled on the ground. The relative accuracy by aerotriangulation is 
0,2-0,3 mm (on the map-scale) and 0,5-1,0 mm — by the slotted — tem- 
plate method. 
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