Jason, sorry I am confused on the tile size. Are you saying the tiles should be 100 x 100 meters? Or 20x20 Meters?

I will work on skybox designs till the designers and coders establish tile sizes before I model anything.

One note, I was thinking it would be neat to be able to design buildings with track component in a tile. For example tunnels
or building bridges with track underneath. So having a uniform tile size for both city and track elements could be very beneficial.