For the reproduction by diazo-copying or offset-printing 
a screening of the orthophoto with a contact screen is 
necessary. For the diazo-copying a screen with 50 to 60 
lines per cm, for offset printing a screen with 60 to 
80 lines per cm can be used. 
The Orthophotomap for Preliminary Design. 
  
An orthophotomap at scales 1 : 5 000 or 1 : 10 000 with 
contour lines at intervals of 1 m or 2 m is an almost 
ideal base for pre-planning of highways and location of 
the centerline. Compared with a line map the very high 
information content of an orthophotomap saves nearly all 
inquiries on the ground. The "terrain on the drawing table" 
in the form of a scaled photomap enables the highway engi- 
neer to identify and locate all important details more 
easily and more certainly than in a line map. Only infor- 
mation about the soil features has to be obtained by in- 
spection on the ground and by drilling. The photomaps, 
produced in several countries in addition to or instead of 
line maps in the scale 1 : 5 OOO or 1 : 10 OOO, are mainly 
used for planning purposes. A very fast map revision at 
periodic intervals with relatively little effort is possible. 
In an off-line operation new photo-flights can be projec- 
ted in the same màp layout, using the recorded profiles 
of a previous flight and so saving a lot of time and cost. 
By this method, in areas with rapidly changing topography 
orthophotomaps for pre-planning and location can be re- 
newed in a short time with little cost. Such photomaps 
with contour lines, slope symbols and break lines of the 
terrain are particularly useful and sufficient in all re- 
spects for highway location. A sample of such a map is 
shown in Appendix 1.