Selecting a Map Projection

Selecting a Map Projection

Cartographers at National Geographic discuss how they select an appropriate map projection for the September 2012 issue.

Grades

5 - 12+

Subjects

Geography

The video above is from the September 2012 iPad edition of National Geographic magazine.

Choosing a map projection is a major challenge for cartographers. Features such as size, shape, distance, or scale can be measured accurately on Earth. Once projected on a flat surface, however, only some of these qualities can be accurately represented. Every map has some sort of distortion. The larger the area covered by a map, the greater the distortion.

Depending on the map's purpose, cartographers must decide what elements of accuracy are most important to preserve. This determines which projection to use. For example, conformal maps show true shapes of small areas but distort size. Equal area maps distort shape and direction but display the true relative sizes of all areas. There are three basic kinds of projections: planar, conical, and cylindrical. Each is useful in different situations.

Cartographers at National Geographic chose to use a version of the Mollweide projection for their map highlighting ocean floors, published as the map supplement in the September 2012 issue of National Geographic magazine. This Mollweide projection is referred to as a pseudocylindrical projection. The specific version of the Mollweide projection used is called an interrupted Mollweide, because lines of longitude, or meridians, are interrupted. The map is pulled apart at specific meridians to minimize distortion in areas where the cartographer would like the map reader to focus their attention.

Find more interactive content, photos, and videos in the iPad version of National Geographic magazine.

Fast Fact

  • The "Map of the Moon," published in the February 1969 issue of National Geographic Magazine, was the first map to show the entire lunar surfaceincluding the far side of the moonon a single sheet of paper.

Fast Fact

  • In 1922, the National Geographic Society adopted the Van der Grinten projection, which depicts the globe by projecting it in a circle rather than a rectangle (as in the well-known Mercator projection) or an ellipse, common in other projections. The Van der Grinten projection was used by National Geographic until 1988.

Fast Fact

  • Many popular online map services like Google Maps and ArcGIS Online use a variation of the Mercator projection. This projection is very good for preserving angles in maps, but is not good for viewing areas of the world close to the North and South Poles.

Fast Fact

  • In 1995, the Winkel Tripel projection replaced the Robinson projection on the Society's signature world maps. Long used in various European atlases, the Winkel Tripel, first published as a map supplement in National Geographic Magazine in April 1995, is one of the most accurate representations of the round globe on flat paper.
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Producer
Sean P. O'Connor, BioBlitz Education Consultant
other
Last Updated

May 20, 2022

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