The earth is round, but a map is flat. How do you get an object that has 3 dimensions onto a 2 dimensional surface? Map projections and the mathematics behind them show you how. But because you are losing a dimension, you also lose an element of the visual representation. Depending on the projection used, the viewer loses at least 1 of the following: direction, shape, area or distance.
An earlier edition of A Dictionary of Geography defines projection as "a technique for transforming the three-dimensional sphere of the earth into the two dimensions of a map. There are four aspects of the map to be considered: area, distance, direction, and shape, and it is impossible to recreate them all in the same map. See map projection.
The subject headings available include "map projection" for general information about projections or under a named projection such as "Mercator projection" or "Peters projection."
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