I have a rectangular mesh but when I go to the UV editor, it is shown over a square backdrop. How can I choose something with better dimensions (i.e. that have less wasted space) and fit the mesh better?
Similarly, when I go to actually export this map, I can choose whatever dimension and aspect ratio I want.
This doesn't make sense to me - why would I export a different aspect ratio than what I just used to set the UV Map?