Thanks for your post. In the current version (Beta 1) there’s no overview map that can be spawned on the screen.
However, in node 35 (we call these glowing info spheres “nodes”) at the main entrance (on the upper floor of the bunker), there’s an animation that not only shows an overview of the bunker, but also allows a view over the entire installation with cut-away walls and roofs.
We understand that this is not a real replacement for an overview mini-map, so we take this as an interesting feature request. We will discuss this and may add it in a future version of FBVR.