I've been pondering this question awhile now... many 3d engines support advanced terrain rendering using quadtrees, LOD... all the features you expect. But every engine I've seen loads height data from heightmaps... grayscale bitmaps. I just can't understand how this is useful - each point in a heightmap can have one of 256 values. But what if you wanted to model Mt. Everest? with detail of 1 meter, or even greater? That's far outside the range of 256. Of course I understand that you can implement your own terrain format to achieve this, but I just can't see why heightmaps are so widely used despite their great limitations.