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Mapping and Projections

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Map projection methods
The systematic way in which a curved surface is represented on a flat plane (such as a page in an atlas) is called a map projection. Three such projection methods are easy to visualize - cylindrical, conical, and planar. If a spherical or spheroidal (or "squashed sphere") object is imagined as a wire-frame model with a light source in the center, the shadows created beyond the sphere can be "projected" onto a flat surface. There are several variations possible with any of these configurations; for example, placing an imagined light source in a place other than the center of the wire-frame, skewing the cylinder, cone or plane to a non-upright orientation, or even allowing the "paper" to "slice" through the sphere. The conic and planar projections constructed as shown in the diagram above are called "tangent projections," because in these cases the "paper" is touching the surface of the sphere without slicing it. The "secant projection" maps (where the "paper" slices through the sphere), are more conceptual and complicated to produce, but are generally preferred over the tangent map varieties, due to the lower amounts of distortion revealed.

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