I've often thought about how I'd best do a map showing depth. Especially your map, since the "grid area" is only at the tops of the tower, and not the ground at all.
I always wanted to try to blur the distant area - making it out of focus. Since the eye is focused on the useable area, the tops of the towers. Don't know if this would work, but its something I've thought about in the past. Probably use a filter to blur the trees and ground structure.