#texture space

Textures do not need to be squares (they can be rectangular if that fits better) but they always follow the power of 2.

If not, the computer will buff out the texture and make it fit which will waste good texture space for other items. See visual example below.

The large square counts for 2048 pixels of memory available for a hypothetical game. The purple boxes are textures not following the power of 2 ratio.

Some games don’t even use textures the traditional way:

 http://polycount.com/discussion/155894/decal-technique-from-star-citizen