Range graded proportional dot map

http://similaritymatrix.blogspot.com/2009_11_01_archive.html

Range graded proportional dot maps are an effective way to visualize variables or things subject to change. They are often used to portray different populations in certain areas. Range graded proportional circle maps use a set number of circle sizes to map point data. The map shown above is comparing two elements and the amounts of each (represented by the circles) found on the surface of water around New Brunswick, Canada.