I'm pretty new to 3D game development and I've recently embarked upon my first attempt at a 3D world (like one for an RPG or similar). I was wondering if someone could explain how to make maps and put things (buildings, objects etc) in it, for sometihng like this. But most of all, is it possible to make a spherical world map, like a planet? How wold that work? Any help appreciated.

You may want to check www.vterrain.org. They have some good resources there.