Creating workable terrain style maps for the Q3A engine takes some reorganizing of thought, but in many ways is not substantially different from making a halls-and-rooms type of map. The designer still has to be concerned about how much can be seen at one time and give thought to map flow and play. The rules and restrictions that guide conventional map design are still there … it just occurs on a much grander scale. You still have to think about poly counts, that hasn’t changed; but generally speaking, the polys that you will use to make your game terrain are VERY large and less are likely to be seen all at once during a game.
The “terrain” style maps in Quake III: Team Arena do not represent any changes to the Quake 3 Engine. The power to make them work has always been there, unrealized and untapped. What has changed is the way map files are created and processed. These construction techniques rely on changes in the Q3Radiant editor and the q3map program that processes the map files into game files.