National 
the 
France 
survey 
are now 
a d m i n i s - 
main roads 
cover part 
The relief file discussed below, is now being digitized and 
will be finished in 1984. In this age which is increasingly 
involved with computer processing, this file will gradually 
replace the normal base map (at least its altimetric part) 
for those groups having computer equipment. We will first 
discuss the different digitization methods used at the 
IGN-F, then the various applications based on that file, 
almost all requiring the calculation beforehand of digital 
terrain models in the form of rectangular grids (D.T.N1.) 
and finally new developments linked with the launching in 
the near future of the French SPOT satellite. 
RELIEF DIGITIZATION METHODS 
1 . Digitization based on 1:25 000 - scale contours 
Contours and spot heights are the only altimetric data 
that exist prior to digitization ; in addition, the 
1:25 000-scale is the largest one for which the relief of 
the French territory is completely described and this was 
the reason why the IGN-F decided to digitize the contours 
and spot heights on the 1:25 000-scale map. That digitiza 
tion was first carried out using manual digitizers (coor- 
dinatographs), then increasingly with automatic digitizers 
(scanners). 
We will discuss these two methods as well as the correction 
and revision procedures. 
A. Manual digitization 
The equipment consists of digitizing tables linked to a 
magnetic tape unit : each pointing by the operator leads 
to the measurement and automatic recording on magnetic 
tape of the corresponding coordinates, preceded by an 
identification code entered by the operator. 
This method can be applied without problems to point data; 
that is the reason why spot heights are always digitized 
in this manner, independently of the contour digitization 
method. The linear data (contours at the IGN-F) are trans 
formed into broken lines joining the finite number of 
points whose coordinates have been recorded, but their 
digitization is long and tedious (about 900 points per 
hour for the sheets with 20 000 - 50 OOOpoints). This is 
the reason why this method has been progressively aban 
doned except in the following cases : (a) if the reading