Triangular plot

A triangular plot is used to illustrate the percentages of three components where the total percentage is 100%.  This triangular plot depicts voting trends. The axes of the figure show the estimated fraction of the population intending to vote for each of the major parties.

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