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for environmental inputs. In urban regions where those conditions are not 
fulfilled, the role of aerial photography will be more important, since it will 
have to supply approximate information on many planning subjects such as 
population, land use, land use changes etc. 
Geocoding Aspects 
A basic problem when spatial information has to be handled is the way 
in which the locational aspect can be preserved. This may be done by mapping, 
using an address, using an area code etc. In data base terminology this is 
called “geocoding”. For geocoding there are 3 important methods actually in 
use: 
point referencing the co-ordinates of, for example, the centre of 
gravity of a parcel will be used as an indication 
for that parcel (Gazetteer, Great Britain); 
segment referencing the position of an address on a segment of a 
network will be used (DIME — USA, NIMS — 
Sweden, RGU — France); 
grid referencing information is stored by grid-cells (Planning In- 
formation System — Switzerland, Planquadraten — 
Hamburg, USEMAP — ITC). 
A discussion of the merits and demerits of these three systems would exceed 
the scope of this paper. What are important, however, are the different 
demands they have for basic cartography and airphoto use. Both for point - 
referencing and for segment-referencing, the co-ordinates of a large number 
of points have to be defined on an electronic digitiser. This presupposes the 
availability of up-to-date, good quality maps. For point referencing, maps 
should be of a large scale, cadastral type; for segment referencing, specifications 
are somewhat less stringent. In France, successful use has been made of 
1 : 2000 orthophoto maps (Butzbach and Chardavoine 1974), while Dueker 
and Horton (1972) suggest the use for DIME of high resolution 1 : 50,000 
photography. The same aerial photography can supply the necessary road 
classification data. For grid referencing even uncorrected photography could 
be used if nothing else is available. From an old map, points of the existing 
topographical grid may be transferred either by approximate methods or with 
the help of a zoom transferscope. Since the grid method has, in any case, a 
lower accuracy than the other two possibilities, it is less sensitive to these