I'm new to this group, but if your map is wide and able to be extended, seems to me you could allow users to upload entire buildings using CAD drawings. An open source platform for the map with no overwrite functions to prevent destroying other people's work. If not CAD, you could convert them automatically to your graphics format. This way you could sell real estate in the game, which is exactly how real life works. You could also generate income via in game advertising, which is also just like real life. And that's just the start. CAD Vehicles with matching controls, like a real flight simulator. The more realistic you make it, the more people it will attract. Then eventually new worlds, etc. The Matrix.