Mercator projection

The mercator projection is the projection of (part of) the curved surface of the Earth onto a flat sheet of paper, a map. The projection is named after the Flemish cartographer Gerardus Mercator, who introduced it in 1569 in his world map ad usum navigantium (for the use of navigation). It is the projection most widely applied in map making, especially for navigation at sea. Technically, it is a conformal cylinder projection.

The meridians (lines of equal longitude) are shown as equally spaced, parallel vertical lines. The parallels of latitude are mapped as parallel, horizontal straight lines, increasingly spaced as their distance from the equator increases.

The mercator projection is widely used for navigational charts, because a straight line on the map is a line of constant direction, a loxodrome. A loxodrome is a curve on a spherical surface that cuts all meridians under the same angle. A ship that sails a constant course (compass pointing in constant direction), travels along a loxodrome, which on a mercator map is represented by a straight line. A loxodrome does not give the shortest route, which is along a great circle, but the difference between loxodrome and great circle, especially for shorter distances, is small. Ease of navigation outweighs a somewhat longer route.

The mercator projection is less practical for global maps because the scale is distorted; surface areas further away from the equator appear disproportionately large. On a mercator projection, for example, the area of Greenland appears to be larger than that of South America; actually, Greenland's area is smaller than that of the Arabian Peninsula.

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Map Projections, Peter H. Dana, Department of Geography, University of Texas at Austin