Any of the featured maps can be played. Players get a random !map and then one veto each (a chance to hit !map again). They can also just agree on a map they both like and skip this process.
Zero-K forum thread:
http://zero-k.info/Forum/Thread/2918
Brackets will look like this.

Round 1 matchups:
[cD]Godde vs [2up]knorke
sprang vs Antelope
Anarchid vs SinKitty
[GBC]1v0ry_k1ng vs mojjj
[LCC]GoogleFrog[0K] vs DanteLorel
Emblis vs Anthem
SaktothIVL vs [dere]gajop
YurGa vs Licho
Reserve:
Hinoki
@[CoX]Malric