For a social network scientist, Amazon is a great sandbox for experimenting and searching for interesting patterns!
I started mapping book networks in the last century. It was 1998 when an on-line conversation raised my curiosity. Here is the original white paper I wrote about that initial investigation.
After the late Tim Russert brought us the "red states – blue states" meme during the 2000 election I started to investigate patterns of political books. I tried various data collection techniques and found an interesting outcome –- no matter how I collected the data I ended up with highly similar patterns. I use snowball sampling -- start at a known point and follow the data out 1 or 2 steps. Once the snowball sample is complete, I start to eliminate the noise in the network -– I want to find the strong patterns that multiple overlapping networks provide. When the patterns emerge I usually see two strong clusters, with a minor cluster or scattering of books between the two large components. I only color the components after my network analysis software finds the emergent groups in the data –- then it is obvious which cluster is blue and which is red.
Below is the first political book map I published on my web site. It showed the famous red-blue divide that had become common wisdom by 2003. It was ironic, and a commentary on our situation, that the center book -– holding both sides together -– was titled: What Went Wrong!
The sharp left-right divide remained in place for the 2004 US presidential election. Below are two graphs of the same data. The first graph is the emergent cluster view –- those similarly connected are closer together. This map was done about 1 year after the 2003 map above. They both contain many different books, yet reveal a very similar pattern and a strong divide.