Geography Reference
In-Depth Information
Most projections of locations transform three-dimensional locations into two-dimen-
sional locations.
sponds to a
geoid
, the name for the shape with the most accurate correspon-
dence to the actual oblate and irregular shape of the earth at a given time.
Projections have great importance for geographic information because
most geographic information records the location of things and events on a
two-dimensional coordinate system, called a “Cartesian coordinate system”
when the
x
and
y
axes intersect at right angles (see the right side of Figure
3.1). Polar coordinates, which record location in terms of one distance and
an angle from a central point, are also used. Any projection of location from
the round surface to a flat plane causes some form of distortion. This has
important consequences for the accuracy of geographic information or maps
and what you can do with a particular projection.
Traditionally, most topics on cartography start by discussing projec-
tions. Projections are one of cartography's most important contributions to
science and civilization. Projections are, and have been, the foundations for
almost all representations of the earth or any part of the earth. Almost all
geographic information also uses projections. The ancient Greek geogra-
pher and astronomer Ptolemy invented several projections that were used by
the Romans and by others for centuries afterward. Some centuries later,
when European exploration and colonization commenced, because they
were so important to the accurate determination of a ship's location and
showing geographical relationships between mother countries and colonies,
projections quickly became an important mathematical activity. You can
even think of the 400 years between Mercator's publication of his global pro-
jection in 1568 and 1968 as the “golden” years of projections. Although the
choice of these years is somewhat arbitrary, it roughly coincides with the
period of significant European colonization and ends soon after computers
made the calculations for projections a much easier task. Before moving on
to the concepts of projections, you should also know that while it is possible
to record the location of things and events in three-dimensional coordinate
systems, they are still rather uncommon in most of geography and cartogra-
phy. They are very uncommon because of their relative complexity, the wide-
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