capacity. At this time the only alternative to achieve adequate progress 
rates in surveying and mapping in many countries appears to be to increa- 
se the degree of efficiency of these operations in the framework of the 
presently available means or of relatively modestly increased means in the 
near future. 
Decisive factors to achieve this as far as the mapping sector is 
Concerned are the map content on one side and map revision on the other 
side. These two factors are so important that we feel it is essential to 
elaborate more on their impact on the economy of mapping. 
A map is a portrayal of terrain features of various degrees of per- 
manency. The amount of permanent features, particularly in urban areas, 
decreases rapidly as a function of time as is illustrated in Figure 1 (the 
curve is the inverse of a geometric progression as permanent features in- 
crease with the inverse of the population increase which follows a geome- 
tric progression). 
Amount of Permanent Features on the Ground 
Time 
  
i | 
20 30 40 50 years — 
Figure 1: AMOUNT OF PERMANENT FEATURES ON THE GROUND 
AS A FUNCTION OF TIME.