WORLD
The map
The world is one shared map with the Citadel at its centre. Distance from that centre sets the zone, so the map gets more dangerous and more valuable the further in you drive.
Cities
Four cities sit in the Frontier. Parking in one gives you a safe berth and access to city services. Entry is judged on your live position, so you can start the request while you are still rolling in.
The Citadel
The centre. Four districts, fought over on a continuous rotation, and the subject of its own page: Citadel siege.