[KaVir]

I don't use a Z coordinate (although I originally planned to have one, and even partially implemented it). There are two types of flight, one is close to the ground (although it's still fast, and ignores terrain penalties for movement) and the other describes you flying up into the sky (effectively teleporting to another X/Y position) and then swooping back down at your destination. Underground locations are simply Things described as "caves" or "stairs leading down" which you can enter.

Things don't block line of sight, although terrain can. Terrain also has elevation, which determines whether you can see it from your current location (described in more detail ).

And yes, multiple Things can occupy the same point in space. Otherwise you get into all sorts of issues with people blocking each other's movement, and I didn't feel it was necessary to go to that much detail to achieve my design goals. I'm not trying to create a 3D graphical game, after all, I just wanted to avoid artificial room boundries for the purposes of combat, movement and communication.