the larger the area mapped, the smaller the scale ratio. The map legend provides
information on the spatial pattern of the data or phenomena that are displayed on
the map. Typically, some system of symbols is used to represent features on the
map. Such features might be tangible (major buildings in a town) or may not exist
physically on the landscape at all (dominant political views in a state; incidence of
a disease by ethnic group, etc.). If individual data points are presented on the map,
then discrete symbols are used. If the data are continuous across the area shown on
the map (such as political attitudes or infection rates), then colors or patterns are
used to indicate the regions where the data are present, or the colors or patterns
may show the degree, level, or intensity of the data. The legend may also feature
a symbol indicating the cardinal direction of north, typically as an arrow pointing
northward. The convention is to place north at the top of the map, and almost all
maps are constructed using this rule, but this was not always the standard. In the
Middle Ages, Europeans often placed east, or the direction of the Orient, at the
top of their maps, and this practice is echoed today in the expression to “orient”
the map—but by placing north at the top!
The projection of a map is a key element that influences how the map appears,
and for what purpose the map should be employed. The two-dimensional character
of a flat map, representing the three-dimensional surface of the Earth, invariably
introduces some distortion. No map can simultaneously indicate true direction,
distance, areal relationships, and angles between two discrete points—at least
one of these properties will be inaccurately represented on the map. Various pro-
jections may be selected that correctly indicate one, or more than one, of these
properties but not all of them. Moreover, projections may be centered on any point
on the globe’s surface, and the point chosen will dramatically affect the perspec-
tive offered by the map. For example, a projection centered on the South Pole in
Antarctica, representing a polar projection, will in addition to that landmass show
only the southern tips of South America and Africa, and most of Australia. In con-
trast, a projection centered on a point on the equator will show all of the Earth’s
major landmasses, but only a portion of each polar region.
Two commonly encountered types of maps are general maps and thematic
maps. General maps are constructed with the intent to convey geographical infor-
mation indicating thelocationand relationship of multiple spatial features on the
landscapeas a reference. Any road map is an example of a general map, as are
topographic sheets (in the United States, produced by the U.S. Geological Ser-
vice), maps showing diverse physical phenomena such as lakes, rivers, mountains,
etc., and maps portraying political states and their boundaries. Maps showing
basic features of an area, such as outlines of countryboundariesor major physical
characteristics, are often used as base maps for mapping other information.
Thematic maps differ from general maps in that they typically are designed to
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