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administratively less known areas (like spontaneous settlements) can be 
monitored in a detailed fashion, both in its horizontal and vertical extensions. 
An interesting aspect is also that the photography remains available. 
Contrary to survey results, photo-interpretation results of a given period in 
the past can be checked again; within certain limits, new classifications might 
be used on the old material, or even information not previously recorded can 
be extracted a posteriori when it is later needed (Hofstee 1971). 
It is this function of an objective document, on which observations can 
be checked, that makes regular photo coverage so important in changing 
urban areas, whether or not they have other sophisticated data systems at 
their disposal. 
4 Desires and Expectations for the Future 
Future developments depend not so much on technological improve- 
ments as on the potential users of photo-interpretation: urban administrators, 
managers, and planners all over the world. These prospective users are often 
not accustomed to the idea of using aerial photography. When they received 
their professional education, this subject was not included in the normal 
curriculum; also, methods of collecting information were usually treated in a 
fragmentary rather than a systematic fashion. In addition, the fact that 
present education may not give yields at a management level within the next 
ten years does not tend to give expectations greater credibility (McLoughlin 
1973). Nevertheless, a cautious prediction should be tried, if only to have a 
picture that can be adjusted to new information. 
4.1 Photography for Urban Surveys 
Black-and-white panchromatic photography is the workhorse of aerial 
photographic applications in urban areas. It will probably remain so for the 
next decade, as availability, compatibility and costs are favourable when 
compared to colour and Colour Infra Red (especially important for 
developing countries). 
CIR has conquered its own terrain of applications: high altitude, small 
scale photography and environmental analysis (including urban residential 
quality and vegetation surveys). The haze penetration capability of CIR, plus 
its ability to differentiate by colour hue gives CIR a relative advantage over 
black-and-white; a number of urban features can thus be identified more