Equal Area World Maps: A Case Study

If one wishes to produce a world map that displays area-based data, such as the extent of rain forests, the range of butterfly migrations, or the access of people in various regions to medical facilities, then it is often appropriate to use a base map that shows the areas of all regions of the earth’s surface in their correct proportions. Such a map is called an equal area or equivalent map by cartographers. A few common equal area maps are Lambert’s equal area cylindrical projection, the Gall-Peters equal area cylindrical projection, and Albers’ equal area conical projection, presented in 1805 and still used by the United States Geological Survey. In this article, we will examine the step-by-step construction of another equal area map known as the Mollweide projection. First announced in 1805 by Karl Brandan Mollweide (1774–1825) and commonly used in atlases today, this map projection represents the whole world in an ellipse whose axes are in a 2:1 ratio. Aesthetically, the elliptical shape of Mollweide’s map reflects the essentially round character of the earth better than rectangular maps. To add to ∗This research was partially supported by the grant NSF-DUE-95-52464