This system allows you to smoothly transition from a "vehicle" unit that explores an "overworld map" area of the terrain, to an "on foot" unit that explores locale maps. In this example you drive around in a miniature siege tank on the overworld, with only a Tech Lab visible: this is a representation of a locale you can visit on foot. You can approach the lab to enter a small area with a bunch of tech labs. Then you can leave to hop back onto the overworld and drive around, discovering two new locales hidden in the fog of war.
Currently this only works for single player. Implementing it for multiplayer maps is very low on my priority list, since I am working on a single player project that required this system.
If you look this over and have any criticisms or ideas on how to make it more elegant, or more robust without excessive work, please let me know!
I had worried about how the minimap and camera movement spoiled the magic. Then I chanced across the Camera Bounds Action having a minimap adjustment feature and everything got better. So, now the camera bounds and minimap size/focus adjust depending on your current position.