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In highway work orthophotomaps are mainly used for 
the following four purposes: 
1. for pre-planning and location of the centerline at 
scales 1 : 5 000 or 1 >: 10 000 
2. for final design at scales 1 : 1 000 or 1 : 2 000 
3. as inventory and maintenance maps at scales 1 : 500, 
1: 1000 or 31 * 2 000 
h. as an aid for the establishment of a data bank 
These kinds of orthophotomaps will be described later on, 
after some information is given on procedures used in 
orthophotomapping based on practical experiences in Ger- 
many. Since the equipment of Zeiss, Oberkochen, in off- 
line operation, is used for orthophoto projection, some 
of the following remarks are influenced by the charac- 
teristics of this system. 
In orthophotomaps the shape of the terrain is generally 
represented by contour lines which, in order to achieve 
  
the necessary accuracy, are better obtained by stereo- 
conpilation in the analogue model than from droplines. 
The accuracy of the contour line and the exact matching 
with the orthophoto even of minor topographic features 
is material to highway design. It is unimportant whether 
contour lines are directly drawn, scribed or digitally 
registered and then automatically plotted. With digital 
registration of the contour lines during compilation and 
electronic processing of the data the profiles to control 
the orthophoto projection can be obtained automatically. 
This way, the conventional and rather lengthy procedure 
of orienting and scanning the models in a stereo plotter 
combined with a storage unit can be spared.