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REPORT OF COMMISSION VII 93
The problem of tactical photo interpretation must in each case be consider-
ed in terms of the prevailing factors of time, space and the enemy. The result is
that there is no single method of tactical interpretation which is universally
applicable. In each case the interpreter must know at the outset both his own
and the enemy’s situation and must also understand the general objectives of the
interpretation he is about to perform. It is also important to know the local ter-
rain conditions and to have a background of information as to what constitute
normal activities within the area so that he may better detect any abnormal
activities. For instance, in an operation zone, a road of broader dimensions than
necessary, built in an area far from ordinary communications may be suspect.
Similarly detection of types of construction not normally encountered in the
area or of irrational cutting practices in the forest may provide hints of great
value to the tactical photo interpreter.
The study of so called “comparative photographic coverage" is valuable to
the interpreter in permitting him to see from the successively taken photographs
any variations and innovations which may have been introduced into the area
since the previous photography was taken.
Vegetation and Terrain Analysis. The terrain, considered from a military
point of view influences the conduct of military operation, not only because of
its formal characteristics (configeration, conformation, division into sections,
etc.) and not alone for the type density and distribution of the vegetative cover,
but also, and especially, for several lithologic characteristics, such as permeabil-
ity, hardness, susceptability to erosion, etc.
In many instances the primary purposes of vegetation and terrain analysis
is to identify and assess all those elements which may hinder or facilitate
movement of military units. In such instances it is necessary to determine all
data which will focus light upon: 1. geomorphological characteristics: that is the
nature and form of the terrain; 2. vegetation characteristics, including species
and degree of cultivation of trees, consistency of forest masses, etc.; 3. hydro-
graphic data on such structures as waterways, bridges and canals; 4. road nets,
both driveable and nondriveable, railways, etc.; and 5. coastal characteristics
with particular reference to the capacity of coastal areas to receive material and
personnel.
To determine the nature of the surface of a terrain the photograph should
be interpreted from both a morphological and ecological viewpoint. In the
latter instance a study is made of relations existing between nature and the soil,
vegetal and human environments. From such studies it should be possible to
recognize homogeneous areas of the terrain within which conditions of signifi-
cance from the military standpoint are essentially uniform. Ecological units can
be distinguished in both natural and cultivated terrains, as exemplified by a
comparison of figures 1 and 2. This area, which is southwest of Rome, Italy,
faintly hilly in the Pliocene, was successively covered over with tuff and then
etched with surface water which made it assume its present physiognomy. The
elementary morphological unit reveals a horizontally stratified terrain of diverse
nature, one superficially cuffed and the other, below, sandy and clayish. The
elementary hydrographic unit reveals transforming and demolishing action of
the water which has lowered the old flat level in that zone which is now slightly
hilly (hills of erosion). The basic vegetation unit reveals how the vegetation
(deciduous forest) is planted on the steep bank, eroded from water which has
