ABSTRACT
If the countries in a map of South America were to be colored in such a way that every two countries with a common boundary are colored differently, then this map could be colored using only four colors. While it is not difficult to color a map of South America with four colors, it is not possible to color this map with less than four colors. In fact, every two of Brazil, Argentina, Bolivia, and Paraguay are neighboring countries and so four colors are required to color these four countries. The regions of every map can be colored with four colors in such a way that every two regions sharing a common boundary are colored differently. Coloring the regions, vertices, and edges of maps and planar graphs, inspired by the desire to solve the Four Color Problem, has progressed to coloring more general graphs and even to reinterpreting what is meant by coloring.
