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At this stage some engineers feel able to dispense with contours,but most 
demand contours at a close interval so that they may more easily judge the fit 
of the road to the landscape, and to assist in drainage studies. 
New low level photography is required with a fairly dense network of 
ground control. If the decision has been made to relate the design to the 
existing national framework, the control surveyor!s task is straightforward. 
It also becomes a simple matter to check or extend the control should this be 
found necessary. Control is established by precise traverse and spirit level- 
ling and the surveyor is well advised to leave behind a few semi-permanent 
station markers and bench marks which will be of value later when setting 
out begins. It will be impossible to ensure that the points are sited clear of 
the proposed works because the exact route is not known at this stage. This 
matters little, however, since the function of the points is to provide a frame- 
work from which other points at a density and disposition suitable for setting 
out will eventually be fixed. 
Turning now to the controversy about the comparative merits of DTM 
and cross sections, it must be understood that the DTM is seldom used 
directly in mass calculations, being no more than a ground model from which 
cross sections are interpolated. So the argument is not really for or against 
cross sections, but rather how they should be obtained, whether by direct 
observation or by interpolation. In favour of direct observation are the 
following points: - 
1. An extra computational process (interpolation of cross sections 
from the DTM) is avoided. 
2. Errors arising from the interpolation of cross sections, affecting 
both volumes and stake lines, are avoided. 
3. The spacing of cross sections and the frequency of offsets can 
be adjusted locally to suit the terrain, so that no wasteful 
observations need be made. 
4. Directly observed cross sections are more readily accepted 
by contractors.