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Materials for the base of the finished maps are durable and as scale 
stable as feasible. It is desirable practice to keep the size of finished maps 
uniform, convenient, and suitable. The scale of these maps should be adequate, 
but not larger than necessary, for the engineering purposes, rights-of-way 
delineation, and transfer of the designed highway therefrom in preparation of 
construction plans and in staking the centerline on the ground. Generally, the 
scales used are as listed in table à. 
Table 4. — Map scales for preliminary surveys 
  
  
  
  
  
  
  
  
Topography Land use Scale 
Feet to one Representative 
inch fraction * 
Rugged Rural, little 200 or 1:2,500 or 
mountainous or none 100 1:1,250 
Rolling to Rural and 100 or 1:1,250 or 
rugged variable 80 1:1,000 
Regardless of, Urban and 50 or 1:600 or 
(unless relief intense 40 1:500 
height to flight occasionally larger scales 
height ratio are used 
makes use of 
smaller scales 
necessary) 
Not applicable Structure 20 or 1:250 or 
sites 10 1:100 
often attained by enlarging smaller 
scale maps; enlargement, however, 
is restricted to not more than 
admissible by accuracy needed for 
structure design 
  
  
  
  
*Representative fractions listed in table are specifically applicable to the 
metric system ‘of measurement, as they are sometimes slightly different in the 
foot system. 
A contour interval which is adequate, but not smaller than necessary for 
the engineering purposes, is used. The interval is governed by map scale and 
ruggedness of topography, minuteness in which the surface configurations of the 
ground must be delineated, and the accuracy required. Besides such limitations 
to contour interval, there are photogrammetric factors affecting balance 
between contour interval and map scale. An economic balance is achieved when 
the contour interval, in feet, is 1/40 map scale in feet to one inch, or the 
contour interval, in meters, divided into the denominator of representative 
fraction expressing scale yields a quotient of 1,575. An economic balance does 
not exist when the preceding conditions cannot be met. Imbalance is often 
essential in fulfilling engineering requirements, and whenever this occurs 
photography scale is set by whichever governs, map scale or contour interval, 
as explained previously in the section on route photography. 
te Ene STI S 
  
  
  
  
  
  
  
  
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