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Decision Support System for Map Projections of Small Scale Data


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  • Mollweide Projection


            The Mollweide projection is an equal-area projection of the Earth within an ellipse. It was presented by Carl B. Mollweide in 1857 and has been called Babinet's Equal-Surface or the Elliptical projection, but it is most often called the Mollweide, Homalographic, or Homolographic.

            It has inspired the Homolosine projection, Van der Grinten projection, and the Boggs Eumporphic projection. It did have a smaller influence with other projections, especially pseudocylindrical, some of which have lines for poles.

            The Mollweide projection only has two points on it that are completely distortion free, lattitudes 4044'12" N. and S. on the central meridian, thus, it is usually used as a world map, at a small scale, and occasionally for a very large region such as the Pacific Ocean.

            The Mollweide projection is shown in an ellipse with the Equator, its major axis, twice as long the central meridian, and its minor axis. The meridians 90 east and west of the central meridian form a complete circle. All other meridians are elliptical arcs which, with their opposite numbers on the other side of the central meridian, form complete ellipses which meet at the two poles. The central meridian is the major axis of meridian ellipses less than 90 from it, and a portion of the Equator is the minor axis. Meridians greater than 90 have the reverse arrangement for their axes. Meridians are equally spaced along the Equator and along all other parallels. The 90th meridians form a circle.

            The parallels of latitude are straight parallel lines, but they are not equally spaced. Their spacing may be determined from the facts that the projection is equal-area and that the 90th meridians are circular. As a result, the regions along the Equator are stretched 23 percent in a north-south direction relative to east-west dimensions. This strectching decreases along the central meridian to zero at the 4044' latitudes, and becomes compression nearer the poles. The distortion near the outer meridians is considerable at high latitudes, but less than that of the Sinusoidal projection.

    * Usage information source:

    Snyder, John P. Map Projections - A Working Manual Paper U.S. Geological Survey Professional Paper 1395. Washington: United States Government Printing Office, 1987.

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