Spent some time today to implement an overhead minimap, which is actually a feature I am still on the fence about. I remember at times in other games when I just spent too much time watching the minimap. It pulled me out of the game somewhat, and I'm not sure I want that for this game. I think there is something to be said for a game where you live in the game view, and where you have to rely on memory and observation rather than an over-map. But I put it in there, and when the time comes I'll observe players and see how they use it as well as how often they use it.
The minimap lives in a second scene structure, one that has its own camera with an orthographic projection. By adding a MinimapMarker component to any object you add a marker to the minimap that will track that object's position. You can specify a model and material to use for the marker; currently, I just use a basic hex model and a solid color, partially transparent material, but eventually I might switch to small icons or something instead. The map tracks the camera position and orientation around the vertical axis, so that directions in the view and the map match up. I have to admit that it does help with navigating the map, so it just might end up being a feature, regardless of my personal ambivalence toward minimaps in general.