The global map was adapted from one in World Population: A Graphic Simulation of the History of Human Population Growth, a 2003 video produced by Population Connection (www.populationconnection.org). In the map, each dot represents a million people. In areas where populations are widely dispersed, dots are placed in the middle of an approximate range.
When areas become super-populated, as they begin to do in certain parts of the world in the 20th century, the dots merge and spread outward like a stain. As a result, some dots may appear in places that are not in reality densely inhabited; even countries or regions that appear "filled up" in later maps may still have sparsely populated regions.
Sources for the graph entitled "World Population Growth, 1800-2050," which appears at the end of the series, are the United Nations, World Population Prospects, The 2003 Revision, and estimates by the Population Reference Bureau (www.prb.org).
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