There's a type of Renderable called the GeometryRenderable; this contains a Geometry object as well as some material data (shaders, textures, special effects) to determine how to draw it. You install this Renderable into the scene information, and then it gets shuffled into the draw buffer and used when it comes time to render your frame. Fun!
This isn't too advanced, but it is pretty necessary. I'm also considering adding polygon splitting so I can use it for map culling, but that should probably be the responsibility of the map generator rather than the Geometry class itself, as splitting is a rarely required task.
Basically, all this rambling is just to make sure I don't break up the posts this week; I think I'll try to make one entry each day this month. Can I do it? I hope so.
Today's link: the science of gangsta rap.