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triangular planes. Although this latter technique gives good ground 
definition the ground can best be defined by a combination of con- 
tours for the definition of smoothly undulating ground and feature 
lines for the definition of irregular or acute ground profiles such 
as existing roads, railways and the like. 
The new English system MOSS, MOdelling SyStems, is a computor sys- 
tem for storing, manipulating and displaying geographic informa- 
tion, or co-ordinated information. The information is stored as 
strings of points representing features which form models of surfa- 
ces, features or networks. In the case of ground models applica- 
tions allow their creation from ground or aerial survey or a combi- 
nation of both. The highway applications permit the design of mo- 
dels of the new construction and volumes are determined between 
this surface and the ground surface. The string concept allows the 
modelling of the most complex interchanges and earthworks from 
which the volumes can be very accurately determined. The MOSS-sys- 
tem was presented as a paper "MOSS - A Modelling System for Highway 
Design and Related Disciplines" prepared by Mr G S Craine et al 
from Durham County Council, England, at the Public Works Congress 
in 1974. The system was launched at a national English conference 
in January 1975. It is reported to have been very well received in 
Britain and at least half the country are using it. The string 
ground models are used extensively throughout Britain for both pre- 
liminary design studies at 1:2 500 scale and at 1:500 scale for de- 
tailed design. Revision of the British D.0.E. survey specifications 
in order to include also string models in the specifications are 
under preparation. The system is also under introduction in some 
Australian states, as in south Australia. 
The progress described above has been reported by Mr Gordon Craine, 
B.5c., C. Eng, from the Durham County Council, England. 
  
  
  
Digital ground models are used in the design of practically all new, 
major roads in the United Kingdom. The motivations for use are that 
road designers frequently make changes, large and small, to their 
alignments as the design progresses and as more data and information 
become available. Digital ground models allow such changes to be made 
conveniently and without re-running the survey which costs time and 
money. Designers also use cost-reducing techniques which combine 
manuel shifts of the horizontal alignment and automatic optimization 
of the vertical alignment; automatic optimization of both horizontal 
and vertical alignments is currently under testing and development, 
and it will make further demands on the use of digital ground models 
especially in the early stages of design. 
  
There have been no major problems with digital ground models apart 
from some early difficulties in checkning for errors in the survey 
data which have been largely overcome. 
In March 1975, the Department of the Environment and the County Sur- 
veyors' Society published Phase 3 of the British Integrated Program 
System for Highway Design. It contains an improved square-grid model, 
a string-line model and a triangels model; the last two models are 
new additions to BIPS so as to give road designers models suited to 
different purposes, the triangels model being for use in land survey. 
Some research continues to improve these models and the selection of 
best models for different circumstances.