concept is essentially an extension of the digital cross 
section technique already described, At present cross sections 
are taken only on lines perpendicular to preselected route 
alignment. This means that if the alignment is changed, the 
stereo model must be set up again, new alignment sheets plotted, 
and new cross section data recorded, before the computer can 
perform its earthwork computations, Consequently to evaluate 
ten trial lines is essentially ten times more work than a 
single line. The entire system is one of replacement of con- 
ventional techniques by exactly corresponding measurements made 
photogrammetrically, and computations and plotting performed 
electronically. 
Professor Miller proposes to utilize to the fullest extent 
the efficiency of photogrammetry in obtaining large quantities 
of terrain data and the ability of the computer to process large 
volumes of data, In short, he intends to digitize the entire 
area covered by the aerial photography. 
In order to do this, a base line is established at one 
edge of the area, This is tied to a ground recoverable 
reference system such as the state plane coordinate system, 
Profiles normal to this base line are then read at suitable 
intervals, and the x y z coordinates of each point are stored 
on tape or cards for use in the computer. It is apparent that 
a combination of the Stereomat and the Integrated Mapping 
System would be ideal for acquiring these numerical data. This 
single set of stored terrain data could be obtained in advance 
of detailed consideration of the location of the highway align- 
ment. The same data could be used to evaluate numerically any 
chosen horizontal and vertical alignment within the digitized 
zone, 
An important consideration in the Digital Terrain Model is 
that each observed point may be given one or more classifications 
for storage in the computer along with its positional co- 
ordinates. These classifications might be such items as: type 
of soil, depth to bedrock, cost of acquisition, etc. These 
classifications could conceivably be extracted from the 
stereomodel during scanning, or, more realistically, supplied 
by other analysis which may be completely independent of the 
photographs. 
The utilization of such a concept is limited only by the 
engineer's imagination or the sophistication of the program- 
ming and computation which he is willing and able to provide. 
Suppose that he assigns relative values to directness of route, 
cost of acquisition, cost of construction. In addition he 
would want to specify such items as limiting grades, sight 
distances, degrees of curvature, areas in which, for one reason 
or another, the highway could not go. He would feed this in- 
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