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FIG. 3. PRESENT WORKING SYSTEM 
season and the following recess work from the subsequent operations 
in the second field season. The models from existing photography 
in the areas where projects for development are likely to be taken 
up should be controlled by E D M traverse or trilateration and 
aerial triangulation by analytical methods. The controlled models 
should be stored for use for the planimetry of the area taken up 
for development. The contour survey can then be done by ground 
methods or on large scale photographs ordered as soon as the pro 
ject details are finalised. 
Actually the contour interval for most engineering surveys is 
so small that ground contouring will work out to be comparatively 
less time consuming. However, the economics of both the methods 
can be worked out in each case and the most suitable one can be 
adopted. 
STANDARDIZATION OP AERIAL PHOTOGRAPHY SCALES 
The scales of aerial photography should be standardized keeping 
in view the cost and time of map production, constraints of flying 
heights and requirements of indentors. The following scales are 
recommended.