At least CP can discovered by a "Google Street View" in detail.
I think it could be done. With a lot of clipping for the buildings and scenery which aren??????t near the external camera. Most common projects are deep into details (which is a good thing) so i think for a really big project, simple buildings would work as well. Maybe colored but without all the detailed windows and fences. As i made a test, i build the entrance area for CP in less than 30 minutes. So the workflow would also very fast. After you??????ve got the general shapes and layout.. you could go back to different areas to add details (inclusive clipping). Clipping is a very powerful technique for optimizing the scene. It does not change the object into a low poly object as the LOD??????s do.. it simply fade out the object. From far away, you??????ve still the shape for the building and if you come closer, the details for the area fading in. This also could be benches, trashcans, lights and so on. Even trees could optimize the scene if you having a big forest and the half of the trees have a clipping-distance from the far away position.
There is a lot more what you can do, to get such a beast up and running!
The most important point maybe is to get started and don??????t get lost in all the details =)
Only some thoughts.