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it has been shown that it is possible to use aerophotogrammetry to make 
in an economical fashion topographical maps, with contour line, of these 
areas, which are mostly covered by thick jungle. These maps are sufficiently 
acourate for the preliminary planning of civil engineering works and for 
making estimates thereof. 
The air photographs of such areas must not be on a scale larger than 
1 /40.000. The scale of the map can in general not be larger than 1 /20.000 
and the distance between the contour lines so smaller than 20 m. 
The above limits are in connection with the thick jungle vegetation, 
which makes it impossible to see the terrain itself. 
In mapping with a stereoplotting apparatus the measuring mark is made 
to coincide with the surface of the trees; in order to obtain a contour-line 
map of the terrain a correction is made for the heights of the trees which is 
obtained by measuring as many a possible of these heights in each stereo 
scopic model, at clearings or along rivers. 
The deviation of the actuel heights of the trees from the average value 
assumed by the above methode causes an inaccuracy which prevents a 
smaller distance than 20 m. being maintained between the contour lines. 
It has been proved in practice that a distance of 1 00 km. between the 
ground control points is acceptable. As far as the elevations are concerned, a 
greater degree of control is desirable, but if this is economically impracticable 
owing to the inaccessibility of the terrain, it is sufficient to make use of the 
level of the sea and of the lower reaches of the rivers and the general course 
of the drainage in the area in question. In this case there is a chance that the 
reference plane for the elevations will have a slight inclination, but this 
should in general cause no difficulties in the preliminary planning of civil 
engineering works. It has been shown from measurements taken on the 
terrain along constructed roads, which had been projected on topographical 
maps made in the above manner, that the deviations in the heights are in 
general no greater than half the distance between the contour lines. 
Apart from this above mentioned mapping, the air photos are used for 
interpretation so that, using the types of vegetation as a guide, the various 
types of swamps and other features of the terrain can be distinguished. 
APPLICATION DE LA PHOTOGRAMMÉTRIE POUR FAIRE LE TRACE 
DE ROUTES DANS DES RÉGIONS TROPICALES 
par l’Ingénieur B. Scherpbier 
N.V. De Bataafsche Petroleum Maatschappij 
Groupe Royal Dutch/Shell 
Résumé : 
De plusieurs régions tropicales il n’existe pas de cartes sur une échelle 
suffisante pour permettre le tracé de routes ou l’étude d’autres travaux de 
génie civil.