The New York Times today released an informative yet beautiful infographic titled "Over the Decades, How States Have Shifted" [nytimes], designed by Mike Bostock and Shan Cartner. The interactive, vertical Sankey diagram reveals the party-based voting patterns of all US states during the last presidential elections.
The more a state is positioned to the left, the more democratic it voted. Vice versa, the more to the right, the more republican. As a consequence, the middle part of the graph contains the so-called "swing states", the states that tend to sway from one political party to another.
By exploring the diagram, one can observe several interesting patterns (some of which are described in the left column), such as to how Ohio always voted for the winner since the year 1964, or when the Southern states started to vote more towards Republican.