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Transactions of the Symposium on Photo Interpretation

about 200,000 square miles of photography to these figures. Fig. 1 shows the
approximate areas of photographic coverage from all sources, both recon
naissance and mapping, in 1962.
Because of the large area of Antarctica, almost 6 million square miles, and
the problems of logistical support, complete standard optical photographic
coverage of Antarctica, even for 1 : 1 million-scale mapping, would be expen
sive and is probably unnecessary.
Mapworthy and featureless terrain can be essentially distinguished by
interpretation of reconnaissance photography. Photo interpretation is used in
a variety of problems in delineating landforms and identifying unusual ice
features in topographic mapping. Finally, photo interpretation is used as the
basis for symbolizing ice features by pictorial and shaded-relief treatment.
The application of photo interpretation
Defining the mapworthy areas
A mapworthy feature may be defined as a prominent, conspicuous, or
essential part of the landscape. It should have some permanent value to the
map and its size and shape should be consistent with the scale of the map. One
of the tests of a mapworthy feature is its ability to serve as a landmark at the
scale of the particular map; if it could not be recovered or recognized at some
future time either on the ground or from the air, its value to the map would be
limited. The following features are generally considered by glaciologists to be
mapworthy for 1 : 250,000 and smaller scale mapping:
Crevasses, crevassing, dark ice, disturbed ice, escarpments, glacial moraine,
glacial shear moraine, glaciers (valley and channel), ice cap, ice-free or ex
posed areas, ice cliff, ice wall, icefall, ice ramp, ice shelf, ice sheet, ice tongue,
ice peaks, lakes and meltwater streams, moraine (also glacial moraine), nun-
ataks, rock outcrops, shoreline and indefinite shoreline.
Features relating to the sea ice such as open leads in the offshore ice, pack
ice, ice islands, floes and icebergs, are either too indefinite or appear only as
seasonal features, and, in general, need not be shown. An exception may be
made for bergs that result from a glacier’s calving; they are mapworthy fea
tures [Charlesworth 1957].
The problem of distinguishing between mapworthy and featureless terrain
may be made less difficult by introducing the concept of the marginal zone of
the ice cap, the zone where surface disturbances are caused by bedrock relief
forming rolling surfaces, crevasses, and nunataks. In contrast to the center of
the ice sheet where the surface is generally flat and smooth, the marginal zone
is marked by landforms, ice and snow disturbances, and meltwater features.
Crevasses can be expected practically everywhere in the marginal zone.
L. M. Gould [Gould 1949] divides the marginal features into three types:
1. The vast undulating, terraced, and crevassed sheets moving into the sea as
an unconstricted or unconfmed wall of ice; 2. the restricted or directed tongues
of ice (valley glaciers and extensions); and 3. shelf ice.