Triangular Plot

http://www.ex-parrot.com/~chris/wwwitter/20050407-it_doesnt_matter_how_you_vote_either_way_your_planet_is_doomed.html

It is also known as a ternary plot. It is a plot of 3 variables. A triangular plot is graphically showing the rations of the 3 variables as positions in a equilateral triangle. All three variables must add up to the constant.