Take a look at this fascinating visualization of U.S. senate agreement groups made by Ph.D. student Adrian Friggeri. Using a complex agreement algorithim based upon data from GovTrack.us, the visualization displays how much all 100 senators of each U.S. Congress during the last 15 years have crossed the aisle –– or stuck to party lines –– on senate-floor votes.
From a design standpoint, the visualization is nearly flawless. The thin red and blue lines help the user form an instant party association, and the light gray bars in the background distinguish each Congress from the next without leading to visual clutter. What's perhaps most impressive is that, despite the fact that the visualization contains far more than 100 different data points, the information is still fairly easy to access and the interface is stil simplistic in feel. Because each Senator's entire individual trajectory is highlighted on mouseover, users can get a glimpse at how willing their respective Senator has been to negotiate a compromise across party lines over the years.
Most of all, the visualization does what all good visualizations should do: tells a story without text. As we can see, the number of Democrats who have crossed the aisle is notably larger than that of their GOP counterparts. This becomes ever more clear when we drill down to look at each party's trajectory individually, where the connections can be seen more clearly. Perhaps what I would've liked to have seen in addition, however, is some sort of summary or average value of the disparity between the two parties on agreement rates, even if just a number at the bottom of the visualization. As it stands, the user has to dissect the visualization a good bit to tell that Democrats have a higher "agreement rate" than Republicans.
The networked line structure reminds me a lot of the Wall Street Journal's "What They Know" visualization, except that this visualization has a good bit less clutter and complexity, and much better styling choices.