the SEABEEs will generally concern topographic
maps for use in construction.
HYDROGRAPHIC MAPS. A hydrographic
map shows the shorelines, the location and depth of
soundings, and often the topographic and other
features of lands adjacent to the shorelines. It also
shows the locations of both horizontal and vertical
control in the area.
SPECIAL-PURPOSE MAPS. These are maps
developed for specific purposes. A PRELIMINARY
MAP developed from a preliminary survey of a
highway, a LOCATION MAP showing the alignment
of the located line, and a RIGHT-OF-WAY MAP
showing the boundaries of the right-of-way and the
adjacent lands all come under the heading of special-
MOSAIC AND OVERLAYS. The aerial
photographic mosaic is constructed from two or more
overlapping prints joined so that they form a single
picture. Usually, vertical photographs are used and a
maplike result is obtained; however, oblique
photographs may be used, in which case the result is
a panorama. The mosaic has become increasingly
useful in cartography and related fields since World
War I. Large geographic areas may be represented in
this manner with each feature of terrain assuming its
proportionate size. The U.S. Army Topographic
Command has a vari-colored map of the entire United
States and other countries that was developed from
mosaics. The Army calls it a PICTOMAP; this is the
type of map that is generally used in a war zone.
Aerial photographs may be converted into line
maps by the use of overlays. Usually, these are made
by tracing the details from the photograph on
transparent paper or vellum and adding such
marginal data as desired. This line map may then be
reproduced quickly by blueprinting or by lithography.
Figure 11-2 shows a vertical aerial
Figure 11-2.-Example of an aerial photograph.