With phasing, there isnt much need for a flat space anymore. The reason Sandbox and Foundry were flat was because intersecting the map geometry was never intended. If you really need a flat space, use the big room area, or, simply make a flat space. Bungie has given us HUGE walls so make floors with.
What about the canyon? And the big water part that connects the bigger island with the beach? and the forest in the mountains? and .. from what you can see so far there is something for every type of map, and even more, for example, there is a Halo 1 themed tower on the map, you may even be able build a map around it ..
There was an IGN video that showed them flying around out in that area. The callsign was "Out of Bounds" and the "Return to Battlefield" message was shown. Who knows what glitches may be discovered to get around that. Only time will tell.
The canyon is huge open land area and the hole water area is a huge open area. If you mean flat area there is that room which is 3x as wide and 1x as long as griffball arena which you can extend. OR just make a huge flat area anywhere with that huge wall. Also there is that small flat grass spot.
"you can use the exact same save zones that bungie uses to set limits on where players can go" The area could be reachable in forge
Which video? Can you post it? I think its less "possibly" and more "almost certainly". In Forge you can't go "out of bounds". The Safe Zones only effect players in actual games. I'm pretty sure that the boundary line you can see in the water (its a big curve) is the edge of the map. Lots of open water. Then look at this screenshot http://www.bungie.net/images/Games/Reach/images/screenshots/Forge_Bnet/Reach_ForgeworldObjects.jpg Top middle, there's a huge flat object to use for floors and walls there.
Oh, I see now. At Comic Con, Bungie showed us a Safe Zone surrounding Hemorrhage and then flew out of it with no warning off death. So Safe Zones don't seem to effect the player in Forge. That clip was in Forge and the area is indeed called "OUT OF BOUNDS". But thats not a huge problem. There's a similar area on the other side on the canyon and there's still a lot of open space. I mean, you could build your own floor just off of Hemorrhage's ground, stick a Safe Zone around it and the players get a map and a nice view of the surrounding canyon outside the map!
I have a feeling about all the new maps that are going to be created.. There are going to be lots of maps instantly built on the flat area above Colosseum, and maybe some water based maps. (I'm going to build one at the waterfall)