- 4 = 
b. À second factor is the aim of the survey. This aim is determined by purely 
technical factors, and also by factors which can have a political or socio- 
economic character. 
What is the aim of the different phases ? 
An exploratory survey is done to localize areas with potential possibili- 
  
ties for development and to exclude areas for further investigations. 
A reconnaissance survey is carried out to see whether it is worthwhile to 
  
continue and to see in which general direction the development should go. 
From the semi-detailed survey the decision should be made whether the pro- 
  
ject can be executed, 
The detailed survey is done to obtain data for ihe execution of the pro- 
ject. 
c, Available time and financial means were given as answers in some cases. e e 
4. Size of ihe smallest unit 
The answers to this question were far from uniform. The question was not re- 
levant for the civil engineers, the sociologists and the economist because 
they generally do not plot characteristics which can be expressed in area- 
units, 
6 experts (2 geologists, 2 pedologists, 2 geomorphologists) gave the answer 
that the unit to be mapped should have on publication scale at least a width 
cf 1-2 mm for elongated areas, and more circular areas should be at least 
4 x 4 mm on publication scale. If we express this for the different phases 
in the actual size in the field, this means: 
elongated areas / circular areas 
  
exploratory larger than 500 - 1000m / 2000 x 2000m 
reconnaissance larger than 100 - 200m / 400 x 400m \ | 
semi-detailed larger than 25 - 50m / 100 x 100m e o 
detailed larger than 10 - 20m / 40 x 40m 
2 specialists interviewed stated that very important objects which are small 
for representation on a map, should be given either as a symbol or should be 
drawn in an exaggerated form. 
One soil surveyor mentioned that the question of minimum size is ónly rele- 
vant for those units which may have an important influence on future deve- 
lopment. His smallest unit would then be about 1 sq. cm. on publication 
scale. 
AERIAL PHOTOGRAPHS 
1. Aerial photographs as & tool for surveys 
Nearly all experts answered in the affirmative, although there is a con- 
siderable difference in ideas regarding the intensity of use of the photo-