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- 6; 
As far as the scale of the photo-mosaics is concerned, scales smaller than 
the original photo-scale had the highest preference. The frequencies of the 
possible answers to the questions are: 
- larger than photo scale : 1 
- equal to photo scale 2-42 
- equal or smaller than photo scale 9.5 
— smaller than photo scale : 5 
de Âge of aerial photographs 
The answer given to this question was fairly uniform, All experts preferred 
recent photographs, recent meaning not older than 5 years, This time limit 
of 5 years is based on: 
— changes in the area of investigation 
- modern techniques in aerial photography provide better photographs e 4 
Restrictions to the 5-year period were made for areas subject to rapid changes 
(earthquakes, landslides, river displacements, rapid changes in land-use, ur- 
banization, etce)e As far as there were requirements regarding the season, pre- 
ference was given, for tropical areas, to the period just after the rainy sea- 
son or at the beginning of the rainy season. 
6, At what moment are the aerial photographs required ? 
In all cases the aerial photographs were required some time before the actual 
fieldwork started, with a variation of 2 weeks to 6 months, For the agricul- 
turist, the civil engineers and the sociologists 2 weeks to ] month was suf- 
ficient, irrespective of the number of photographs. 
For the pedologists, geologists and geomorphologists the number of photographs 
was important, although there was a considerable range in this number, For a 
period of 1 month, 75 to 150 photographs could be studied, provided that the 
photo-scale was adopted to the survey phase. This range was found in all dis- e | 9 
ciplines represented, 
All the experts affirmed the question concerning the necessity of base maps 
for resources SurveySe 
Le Scale of ihe base map 
The following somewhat divided answers were given? 
= 7 experts asked for a base map on photo-scale 
- 4 experts required base maps on photo-mosaic scale (they required a mosaic 
Scale equal to or smaller than the photo-scale) 
— 3 experts required base maps on publication scale 
— l sociologist required a base map on scale 1:50,000, except for some special 
purposes for which a cadastral map is necessary,