Dot Distribution Maps

http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/plate_tect01.html

     These types of maps are an easy way to depict density of whatever variable is being plotted. The visual clustering of dots shows a high density of the variable occurring while large spacing inbetween the dots shows low density values. This example shows earthquake locations for events between 1965 and 1995. The red dots are shallow earthquakes, the green are intermediate depth, and the blue and purple are deep.