Hm so you would have a world object with several different regions and when you move a unit you (possibly) place it into a different region? Or something along that line...Could someone post a basic class design to show how it would be set up?
typically a section of the world would contain a list of pointers to the entities that are within that particular section. Whenever an object is moved, it undergoes a process called "relinking", where you calculate what parts of the world each object's bounding box lies in, and removing itself from the previous parts of the world it no longer resides in. You do not have to recurse the entire world when you do this.