Where is my Congressman on the spectrum?

Looking up some information on a couple of bills in Congress, I ran across a website called GovTrack.us. If you follow the link to the site's page for an individual Congressman, you'll find something like the energy efficiency label on a new refrigerator, with an arrow pointing to the Congressman's relative position on the political spectrum. This link led in turn to an interesting and immediately understandable graph:



There's a pretty comprehensive description of how the positions were determined -- but basically, it comes from the bills which the Congressman or Senator co-sponsored. I'd like to see the same just for our delegation from North Carolina.