It has long been the rule among map makers that whether a map is drawn on a flat surface or on a sphere, four colors are enough to distinguish countries which have a common border (not merely a point). For over one hundred years, mathematicians have been trying to draw a planar map on which five colors are needed. It was not until 1976 that a computer was used to prove that maps requiring more than four colors DO NOT EXIST. Any map can be colored with no more than four colors.