Outdoors algorithms are extremely different from their indoors counterparts. The focus is no longer on occlusion, but on detail handling, and this makes a huge difference in their design. Indoors algorithms are well understood today, whereas terrain (and especially scene graphs) rendering for outdoors algorithms is still being researched. Currently, most effort goes into occlusion detection for outdoors games. For example, how can we detect that a hill is actually occluding part of the action, and thus save precious triangles? This is no easy question. The amount of data makes this a very interesting question. A quick and easy solution, assuming your hardware supports occlusion culling, is to render the terrain front-to-back before rendering any other objects such as houses and characters. We can then use the Z information from the terrain to drive an occlusion query phase. But this is not a perfect solution. Thus, many teams are working to incorporate concepts such as PVS and view distances into outdoors scene graphs. The complexity of the problem definitely makes for an exciting challenge!