Right, that's what I ment when I said "put them in their own level" and compile them to map entities. Not have seperates "zones" or "levels" for interiors.

EverQuest has a single compiled map file for the level. The original EQ zones are pretty low polygon in an of themselves. When zoning they use the classic "can't see around the corner" bottleneck.

Each "zone" in DAOC is a terrain square. I believe they unload the other terrain squares when they are out of sight. They also use the bottleneck zoning for things like the main cities and dungeons. Because they use terrain and not BSP, the buildings themselves probably pop in and out at the clip plane (which would be map entities).

Keep in mind that the farther from 0,0,0 you get the slower BSP goes.

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Another trick I thought of to squeeze more space into 3DGS levels would be to stack walkable areas vertically. You enclose each section of Z in a sky box so you can not see the other sections above and below.

So city #1 might be 50000x50000 at Z 0 and city #2 might be 50000x50000 at Z 10000.

City #2 [--------------------------] 10000 Z
City #1 [--------------------------] 0 Z
Forest [--------------------------] -10000 Z