INTRODUCTION 
A Digital Elevation Model (DEM) is herein defined as any 
machine readable (digital) representation of a topographic 
(elevation) surface. This definition does not restrict the 
term DEM to regular square grids, which are but one example 
of such representations. Following current practice, the 
term "digital terrain model" is used when the mode includes 
other "terrain" aspects such as materials, soils, vegetation 
or traffic ability, in addition to simple elevations. 
Digital Elevation Models have a large number of military and 
civilian applications. Some of these applications include: 
a) Production of topographic maps from survey or photo- 
grammetric data. .An increasing number of automated or semi- 
automated topographic mapping systems include a DEM in the 
compilation and editing systems. Unfortunately, many of 
these systems then "throw away" the DEM after a printed map 
has been produced. DEM's are essential in the computer 
production of three dimensional surface views of topography. 
b) Engineering calculations. Initial calculations of 
reservoir volumes, cut-and-fills for highways, and other 
engineering calculations may be greatly facilitated by DEMs. 
c) Line-of-sight calculations. Determining whether one 
point is visible from another has many applications. Civil 
ian uses include determining locations for forest-fire 
watch-towers (maximum visible area desirable) or logging 
clear-cuts or power lines (minimum visibility desired). 
Military applications are obvious (locating lookout or 
command posts at points of maximum or minimum visibility, 
respectively, are only two examples). Furthermore, the 
straight line may be replaced by other curves to plot tra 
jectories and determine potential target areas. 
u) Urban and regional planning. Certain problems related 
to planning, such as sewer line locations, can be facil 
itated through the use of DEIi's. 
e) Navigation. Ily combining a radar altimeter with an 
on-board computer and DEM, it is possible to use profile 
mate.ing techniques to aid in navigation of manned and 
unmanned aircraft. 
f) Components in complex models. Near shore ocean bottom 
topography is an important element in oceanographic models. 
DEM's can be useful in this regard. Also, nyurologic 
models for snowmelt-dominated drainage basins require a 
topographic component. 
g) Geomorphology. Digital Elevation Models may be used in 
the computation of a variety of descriptive geomorphometric 
parameters which are useful in a variety of pure and 
applied applications. 
h) Geographic Information Systems. Topography can be an 
important element in a GIS. In these systems other