Every four years, Valdis Krebs, an expert in network analysis, takes a look at the political book-buying habits of Amazon's customers, and performs a bit of data visualization magic. By looking at the data Amazon shares about people who buy books in common, along with the "also-bought" pairings, Krebs produces a network map linking books, and their buyers, into clusters. You can see the moats dividing many Americans into blue and red islands, but also the places where intellectual bridges may exist. (I've included a snippet of the map, but to see the full picture you should go to Krebs' website.)

There's some good news here for anyone concerned with the seeming hyper-polarization of politics in America, for the first thing Krebs found is that compared to 2008's book network when there were no connections between the red and blue book clusters, this year's map shows several connecting points.

 I thought the map would show each group honing up on their side's talking/debating points and ignoring books of non-conforming opinions.  I was surprised, the two clusters were connected in October 2012 -- by several books!  The hub in the center of the network, with spokes to many blue and red books, is The Price of Politics by Bob Woodward.  Woodward is viewed as a center-right journalist, so it makes sense that both sides would be reading his usually excellent prose.  No Easy Day, by one of the Navy Seals that took out bin Laden reads more like a novel, than a history book, attracting readers from all political persuasions.  The third bridging book is a surprise! The Little Blue Book is intended for a progressive audience -- it is a handbook for how to argue effectively with the other side.  So, you would expect it to be firmly in the center of the dense blue cluster, right?  Wrong!  It has both blue and red readers!  The other side is probably trying to understand their opponents and reading their blue handbook -- similarly to how they read the far eft book Rules for Radicals during the 2008 election campaign.

If you drill further into the map, it's fun to see which books sit closer to the center and which are further out on the political fringes. Jeffrey Toobin's "The Oath" and Michael Grunwald's "The New New Deal," for example, are closer to the center than Chris Hayes' "Twilight of the Elites" or Paul Krugman's "End This Depression Now." And the "red" titles are also more uniformly focused on vilifying Obama than the "blue" ones, which include several historical titles on subjects much further from the upcoming election.

The second fascinating finding is how different people are relating to the books written by and about the candidates directly. In 2008, Krebs discovered a stand-alone cluster around President Obama's two books, "Dreams From My Father" and "The Audacity of Hope." People were reading up on the new candidate, apart from consuming political books. In 2012, Obama's books are still being bought, along with Romney's "No Apology" and "The Young Guns," which includes a lot of material on his running mate Paul Ryan. But this presidential cluster is solely connected to "red" book buyers. Krebs comments, "The pattern is positive for Romney -- people reading about him are reading other red books -- not so, for Obama.  People reading his positive biographies and position books are also reading polemics attacking Obama."

Obviously this is not a scientific poll, but more of a look at the current interests of that narrow sliver of people who feast on political books. But it suggests two things: first, that maybe the book-buying elite isn't as divided as the rest of the country. And second, that liberal readers aren't fired up by Obama any more. But we knew that already.