I've been thinking about it and can't really figure it out. Not enough information.
So, lets pick a game. For example, World of Warcraft or Diablo III.
I suppose every location starts off with a number of sketches or even matte paintings done by a concept artist. It will establish general mood and a number of key points of interest.
Then comes a level desiger and draws general maps in Photoshop, shares with game designers, draws again and so on until he can finally get his hands dirty and start building actual level.
Obviously, in World of Warcraft and Diablo III there is sculpted terrain which could be done only by level designer. But what about architecture and all other assets? Will level desiger model and texture walls, arcs, stairs and so forth? Or does he do rough sketchy 3d models for an environment artist to come forward and build high quality assets based on the level desiger's needs?
And if the level designer is responsible for building rough 3d models, how detailed should they be? For example, in Diablo III there are dozens of different kinds of walls, with or without decorations, columns, holes, ruined elements etc. Will the level designer make all those little things?