The game world is a 500x500 map of 5x5 mile map squares. each map square has its own d3d coordinate system, with its origin at the SW corner of the map square. positive x is east, positive z is north, and positive y is up. When i first started on drawing terrain graphics, i just made it draw stuff in the player's map square, to get things up and running quickly. then i went back and converted everything to use world coordinates (map x,z + d3d x,y,z) for figuring out what was in visual range, and then converting to camera relative coordinates for frustum cull and actual draw calls. This shot shows fruit trees and dirt terrain as seen from an adjacent map square which is scrub terrain.