By using the new UMBRA rendering technique, the engine now only needs to render what it anticipates the player needs to see, so in the same Windmill, only the interior walls and characters in the area are visible, hence none of the other stuff like the hills and trees are rendered. This allows a massive performance boost for the user (Gordon referenced frame rates of up to 150 fps) to occur, which will hopefully lead to less lag when playing/fighting in large numbers. Pretty cool stuff, as those of you that attend large player raids should be able to appreciate.