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Estimations 
As stated earlier the difference between measurement and 
estimation is sometimes hard to determine, In a measurement 
procedure the use of some constant accurately calibrated 
measure unit is essential, The estimation, again, is based 
more on experiencevise judgement. However, some kind of 
Scale, at least a relative one, is always used also in 
estimation. 
In Tripoli land use survey the distribution of floor space 
use between different economic functions was estimated, Using 
stereoscopic photointerpretation and direct observation in 
the field first the dominating land/space use function of the 
pattern was determined and then the relative proportion of 
the other functions within the same pattern. If none of the 
functions according to the classification had "majority", the 
pattern was classified to "mixed" cathegories or a re- 
patterning was made, 
In the central city where the determination of the dominating 
land use was sometimes difficult (even within one building 
the variation of space use can be high), special field samples 
were taken, Within the field sample area the economic function 
behind each of the windows was estimated and classified and 
the space use distribution determined according to the num- 
ber of windows in each class, The total area of field samples 
represented 10% of the floor space within a traffic zone, 
Photointerpretation 
The stereoscopic viewing of 1:20 000 photos using a Wild 
Pocket Mirror Stereoscope was fundamental. Without the 
stereoscopy this working method would have been impossible,