Cottonball is a large scale objective game map – designed first and foremost with CTF and Assault in mind. The map is almost, but not-quite-perfectly symmetrical. Some natural geology prevents each base from being a simple mirror image of the other.
The map is large enough so that even when a team makes off with your flag, there’s still a lot of ground you can use to catch up. The other is that each side has some wonderful shortcuts – natural and mechanical – that may not make great flag escape routes, but might let a mobile pursuer cut off escapees."
(Quoted from Bungie Weekly Update, 1/18/08)
Also mentioned in the weekly update is that the map is "massive and labyrinthine".
It has been confirmed the map is set on a Halo.
"I guess a game of Big Team Snipers would be possible, but anything else would be comical without vehicles" - Frankie