Really Random March Madness Question

Does anyone know how the brackets are determined? I've tried googling, but have really bad google-fu. I have this idea for a little fandom-ish project thing and need to figure something like that out. I have the rankings, I just need to figure out how to match them all up....

Supernatural Guest Character March Madness Showdown!!

So, I had a thought the other day and I thought it might be fun to do. With all the March Madness stuff going around I thought it would be interesting to see who people think the best guest character is on the show. So, I have made a March Madness Mash Up!!

The initial brackets and standings are based on the number of the characters appearances as of the airing of 4x16.

ROUND ONE WILL CLOSE MONDAY, MARCH 23rd AT APPROXIMATELY 9:00 PM CT. Voting for Round 2 will be up by 10:00 pm.
ROUND ONE IS NOW CLOSED. PLEASE COME VOTE IN THE SWEET SIXTEEN.

**PLEASE REMEMBER THAT THIS IS VOTING FOR THE CHARACTER NOT THE ACTOR**
( Let's Get Ready To Rumble!! )

Please spread the word to your flists. I'd love to get as many people voting as I can. Thanks!!

I will be tagging all these posts the same, so if you want to watch for this tag, feel free to.