Geography Reference
In-Depth Information
A government wishing to pursue developments needs cadastral mapping in
order to assure it knows where it can develop and who should be involved. In
times of upheaval, the cadastral map has also been an aid for taking land
away from groups and individuals and turning it over to others.
Thematic maps, both qualitative and quantitative, are perhaps the most
widely used form of maps. They make it possible to show things and events
that people can otherwise not see nor experience—for example, 2003 birth-
rates in counties, or population per square mile in all fifty U.S. states (see
Plate 9). The major strength of this form of cartographic presentation is that
it enables easy comparison. The birthrate, other demographic statistics, or
environmental statistics, can be presented in a tabular form, but the use of a
cartographic presentation helps with comparisons by making the geograph-
ical relationships plain.
A special type of thematic maps, choropleth maps use a graphic variable
(usually hue or value) to show quantitative differences. They are easily prone
to misunderstanding because they fail to distinguish differences between
subareas of the geographic units shown. For example, a map showing birth-
rates in the 50 U.S. states fails to distinguish urban and rural differences.
Choropleth maps are also erroneously used to show the number of a particu-
lar property for an area—for example, population, cars, or voters. However,
the area of the geographic unit (e.g., state or county) plays a direct role on
how much of the property can be found in an area. No matter how urban an
area is, the number of religious buildings stands in relationship to the size of
the area. The easiest way to avoid this error is to always use choropleth map-
ping for properties of a constant unit (e.g., an acre or hectare). This
approach was further developed as dasymetric mapping.
Charts often stand alone for naval or aerial navigation, but they can be used
in conjunction with maps to provide geographic orientation.
Cartograms, both contiguous and noncontiguous, show quantitative differ-
ence by altering the size of the geographic units according to the relative
proportion of the geographic unit's property (see Plate 10). One type of
cartogram stretches all boundaries to create an image that roughly corre-
sponds to the original, even if greatly distorted. The second type simply
scales the boundaries of each unit according to its rank with other units.
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