Easy! Have the terrain extend with a random perlin effect (which modifies a simple "clamp" effect of having the current height/texture continue to infinity) to the edges of the LOS in all directions. Maybe have it computed at map design times, by adding a screen-width "border" region to the map terrain. Then darken all colors beyond the map region by half, or simply add a colored border around the edges. This solves both problems: It clearly defines the game area, and it is much more immersive (by dint of not ending abruptly in darkness or visual artifacts) than the typical approach would be. In my own project (which has the added challenge of accomodating a landscape perspective in regular play), I extended the ocean visual beyond the range of vision in all directions, then modified my map generation scripts so that, in effect, all maps are islands. (Although a 2x-size terrain might be possible with no framerate decrements) The end result is quite pleasing! The holy grail of map borders, I think, is probably the World in Conflict approach - both terrain and scenery objects extend to the horizon in all directions!