Click on the image below to magnify it. It shows all the current members of the Illinois House and Senate arranged by how similar their bill sponsorship patterns are. Only the horizontal axis has any meaning (placement on the vertical axis is arbitrary). Members who are very close to each other on the horizontal axis sponsor many of the same bills. Republicans tend to sponsor Republican bills, and Democrats tend to sponsor Democratic bills, which is why you can clearly see the two groups separated. This analysis was done by the method of singular value decomposition (SVD). The SVD method is explained very well on govtrack.us. Two outlier members (Michael J. Madigan and Barbara Flynn Currie) were removed because they are very far to the left, and their presence makes the plot harder to read. This image was generated on May 24, 2009.