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practised in the use of computer-aided systems may seek advice on how best 
to integrate the survey process with other design processes, for no two 
projects are ever quite the same. 
Remembering also that the air survey operator may be called upon to 
undertake some of the routine design computations, whether directly or by 
employing a subcontractor, and that often the placing of mapping contracts is 
dependent on the range of supporting services offered, it is obviously to his 
advantage to acquire a knowledge of the whole system in some considerable 
detail. 
It is therefore the object of this paper to outline the present state of 
development of the design process and the photogrammetrist's role in that 
process, and to warn of some of the pitfalls awaiting users of computer-aided 
de sign systems. 
THE DESIGN PROCESS 
From conception to completion, a road project passes through four 
stages, scheme stage, design stage, tender stage and construction, of which 
we are here concerned with the first two only. 
Scheme Stage 
Scheme stage covers all work up to the adoption of an alignment, which 
may then be legally fixed. 
Starting as it must do with a broad band of interest, perhaps embracing 
several possible routes, it is clear that scheme stage planning must be based 
on outline rather than detailed information. Much of this information can be 
taken from existing surveys, but often there is a strong case to be made for a 
specially commissioned survey at scheme stage, involving medium -scale 
mapping with contours and perhaps an open-mesh digital terrain model. 
Not only may existing maps be out of date, of unsuitable scale or 
inadequately contoured but, if not inaccurate to start with, they may very well 
become so by the time the engineer has compiled them into strips following the