. men 
-.1074 - 
It is noticeable that obliques are used in considerable 
proportion. From the questionares it is apparent that 12 of the 1: 
userc have had oblicues made by suppliers and ac many ac 6 have hac 
o'liguer made in their own institutions. This high number car to 
^ 
exrlained by the relative iow cost and high flexibility of this technique, 
especially if undertaker ty themselves (QUADFLIEI, 1978). A need which 
suddenly arises cai be quickly met, for example with respect to temporary 
tuztions such as roadworks, perkins congestion, disasters, etc. One 
cf the users, the local authority of Apeldoorn, acts in this re as 
£u 
gar 
supplier and coordinator for a considerably large number of surrounding 
and even outlying local authorities. It is even possible to take to the 
air within one hour of receipt of instructions! 
Colour-infra-red photography is mainly used for analysis of the 
quality of urban "green" areas. Undoubtedly the positive results of research 
into use of this technigue have had some influence here (SIAB,1973). 
Use of colour photography is a rather recent innovation accordins to 
one of the suppliers. One of the local authority users (Utrecht) in fact 
tioned the increase of interpretation possibilities vis-a-vis black and 
hitc. Since the introdunction of colour photography, there has been a 
= 
considerable growth in usage by other municipal bodies in Utrecht. 
In mony caro, more than one sort of material is used. Figure 4 below 
cives an impression: of the various sorts of material used by thc respondents. 
  
  
  
  
  
  
1 19 
number 
2 13 
of 
3 2 users 
4 2 
Figure 4 NUMBER QF DIFFERENT SORTS CF MATERIAL USED 
The scales used are somewhat variable, but there are at first sight 
concent rations around the 1 : 2500, 1 : 5000 and 1 : 10.000 - 12.000. 
On the basis of this observation, a classification has been constructed 
with increasing class intervals and with these concentrations falling 
into different classes: 
Bl 
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PR 
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wh 
al 
sh 
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ta 
re 
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