Then, zone out your areas on the map so they contain info on what their land use is: New commercial districts, old rundown commercial districts, new business parks, old industrial areas, parks, urban hirise living, suburban housing, etc. Then write procedural generators of buildings given this zoning info to place buildings according to the zoning info.
Areas would be generated based on the player''s current location. If the player opts to enter a building, then given info on the building type, you could have procedural generators to ''decorate'' and furnish the interiors of the buildings.
You could even take it a step further. If the player was to rifle through the contents of a desk drawer, you could have procedural generators to populate the desk drawer with items such as a letter opener, a pistol, and so on.