Arthur H. Robinson, John P. Snyder
Barbara B. Petchenik
Design and Production
David DiBiase, Jeremy Crampton, Marty Gutowski
Deasy GeoGraphics Laboratory, Penn State
Special Publication of the
Cartography and Geographic Information Society, a member organization of the American Congress on Surveying and Mapping, 5410 Grosvenor Lane, Bethesda, MD 20814
© 1997, American Congress on Surveying and Mapping
A globe is the only representation of the earth that does not distort its geometry -- except, of course, its size. Unfortunately, for many purposes a globe is an inconvenient way to display geographical relationships: Significant concepts, such as constant directions, shortest routes, and equal distances are difficult to measure on a curving surface. Often we want to see the whole world, but in looking at a globe we see only half. Finally, unless the globe can be turned in all directions, it is difficult to look directly at a region of interest.
The alternative, a map made by methodically flattening the globe surface, modifies its geometry but is easier to make, file, and (especially) use. A systematic transformation of the earth's surface to a flat map is called a map projection.
There are infinite ways to carry out this transformation. The changes that result from flattening the spherical surface are technically called "distortions." This is a rather unfortunate term since it connotes something undesirable. Yet many projection systems can turn the inevitable distortions to our advantage. For example, direct routes can be made straight lines, regions of greater interest can be enlarged, ranges can be shown as circular, directions and distances from one point to all others (and vice versa) can be clearly displayed, areas of interest can be centered, and so on. The sections in this booklet, prepared by experts, illustrate a number of ways to make map projections serve different purposes.
This is the third booklet in the special series on map projections issued by the American Cartographic Association and published by the American Congress on Surveying and Mapping. The first two, Which Map is Best and Choosing a World Map, may be obtained from the publisher.
It is our hope that the reader will be stimulated to understand map projections and appreciate their versatility. They are not really mysterious.