BayCon, from what I've heard/read, is more of a science fiction/fantasy convention held every year. Since many cosplayers also create costumes depicting sci-fi/fantasy stuff, this is one of the big venues where they get to show off their work.
You can read about the programming/details of their most recent one at www.baycon.org
You can read about the programming/details of their most recent one at www.baycon.org