It may not need mentioning here, but … the terrain entity needs to be contained inside a sealed world. For the terrain maps in Q3:TA, we built huge boxes. Any portion of the box that could be seen while playing the game, or flying around in spectator mode was covered in sky texture. Any portion of the box that could not be seen was made out of common/caulk. If mountains or canyon walls surround your map, plan to bring the caulk portion of the wall up as high as you can. This can reduce the number of triangles seen in the map. Generally speaking, you will see ALL the sky triangles inside the map at all times.

      Finally, and this is a part of vis blocking, but it should also be noted here. Don’t forget to place large caulk structures that rise up from the bottom of the world box to near the ground surfaces of terrain entity. If the ground level rises and falls substantially, these can be a part of the vis blocking process. Otherwise they serve to reduce the size of the map’s total volume (generally speaking … a good thing).