Network Analysis Showing Increasing Polarization of American Congress

I came across a very interesting article with a set of network maps of the 101st (1989 session), 107th (2002) and 113th (2013) Congresses. From the article published in the Economist:

"The network maps shown here look at the degree to which senators vote the same way. Each node is a senator. Links represent instances when senators have voted similarly on substantive legislation on at least 100 occasions during the same congressional session. Their placement is determined algorithmically, based on their co-operation with other legislators—which has the effect of pushing more bipartisan ones to the centre."

The conclusion of the analysis, done by a computer science undergrad at Harvard, is not surprising; Congress and American policymaking has become much more polarized over the past two decades.

http://www.economist.com/news/united-states/21591190-united-states-amoeba

http://www.economist.com/blogs/graphicdetail/2013/12/daily-chart