46. Triangular plot

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

Triangular plots show the relationship between three variables that sum up to a uniform whole. For example, this shows the percentage of Liberal Democrat, Labour and Conservative votes in an election. This is useful for political campaigns to analyze the three main parties and see an estimated fraction of the population voting for their major parties. Another good example of triangular plot I've seen is of soil composition and the three variable that soil is composed of.