Geography Reference

In-Depth Information

spread use of two-dimensional coordinate systems, and the cost of trans-

forming two dimensional coordinate systems. Chapter 4 will take a look at

some of these systems, including their applications.

Key Concepts of Projections

Projections convert measured locations of things and events in three dimen-

sions to two dimensions. Projections are important but also complicated

because it is impossible using geometric or more complex mathematical

methods to simultaneously preserve both the shape and the two-dimensional

area of any three-dimensional object found either on the spherical surface of

the earth, in the earth, or near the earth, when we depict it in a two-dimen-

sional coordinate system. Each projection is an abstraction of the earth's sur-

face and introduces distortions that affect the accuracy of the geographic

information or map. A projection starts with one of three representations of

the earth's irregular surface (geoid, ellipsoid, or spheroid) and converts it

directly or through intermediary transformations to a f lat, or planar, trans-

formation.

Choosing the right projection is important for controlling these distor-

tions. Thankfully, choosing the right projection for a particular area is a task

that has often been done by institutions and governments and made part of

World map from 1801 using a Mercator projection.

From
www.davidrumsey.com
. Reprinted by permission of David Rumsey.

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