Range graded proportional circle map

http://www.nature.com/nature/journal/v451/n7181/fig_tab/nature06536_F2.html

Range graded proportional circle map is a type of map that uses circles in order to show the value of a given data in a given area, the size of the circles vary according to the value of the data. This range graded proportional circle map shows the 2008 number of EID events in the World.