In a post about NY congressional candidate Dede Scozzafava, political scientist Boris Shor (who generally does what I do, only better and faster, which is a problem), produces the graph below. Just to explain what this is, Shor and Nolan McCarty have collected the NPAT scores for state legislators in all fifty states. The NPAT (National Political Aptitude Test) is administered by Project Vote Smart. He managed to produce a common scale across all the legislatures. The graph shows the ranges of issue stances within the legislatures.
This graph is very cool for me, in particular, because, well, look how darned polarized California looks! It's got the most divergent parties in the nation. This interests me because some roll call studies (particularly Jerry Wright's data) suggest that California has one of the most polarized legislatures, but not the most. It's occassionally surpassed by Wisconsin, Iowa, and a few others.
What Shor's data show, if I understand them correctly**, is that the ideologies of California's elected officials are the most polarized -- not as manifested in roll call votes, but as simple expressions of issues stances. This gets around the issue of agenda control, by which the majority party can pick votes that make the parties look more divergent than they really are. California's parties have been the most effective in the nation at screening out the moderates. There really is No Middle Ground. (Sorry for the shameless plug.)
*NPATs have a fairly high non-response rate, as I understand it. One presumes, however, that the non-response rate is uncorrelated with ideology or region.
**Late correction: I apparently did not understand them correctly. As Boris explains in comments, the ideal points are, in fact, derived from roll call data. Apparently 15 years of roll call votes from each state legislature. (I really need to know how they pulled that off.) They used the NPAT scores to create a common space across legislatures. So agenda control is still potentially an issue, but probably not a huge one.