Monday, February 19, 2007

World maps and projections

Maps of the world or big areas are often either 'political' or 'physical'. The most important purpose of the political map is to explain territorial borders; the purpose of the physical is to show features of geography such as mountains, soil type or land use. Geological maps demonstrate not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures.
Maps that depict the surface of the Earth also use a projection, a way of translating the three-dimensional actual surface of the geoid to a two-dimensional picture. Perhaps the best-known world-map projection is the Mercator Projection, initially designed as a form of nautical chart.
Airplane pilots use aeronautical charts based on a Lambert conformal conic projection, in which a cone is laid over the division of the earth to be mapped. The cone intersects the sphere (the earth) at one or two parallels which are selected as standard lines. This allows the pilots to plan a great-circle route approximation on a flat, two-dimensional chart.

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