Well I almost understood your post. Ann Arbor would gladly host a jam, we have quite a few active traceurs and plenty of good spots. I didn't see a question or statement in your post but assume you're asking about the most concentrated area as far as number of traceurs. Thing is, very few of us post on the board, we spend our time training.
Also, I'm the 6th sexyest guy in Ann Arbor and always down for "activity"

(I joke, but I shouldn't have said anything, this thread is ruined now)