Help Understanding Unity Terrains

Hey guys,

I am trying to figure out how heightmap terrains work. I have a very simple question:

For a given heightmap resolution of 513 x 513, what is my terrain width and length supposed to be?

Is it 512 x 512 or I should match it to 513 x 513? I don't want any stretching in my terrain, I want it to match perfectly.

Same thing with 1025 x 1025 resolution heightmap, am I supposed to have a 1024 x 1024 terrain width & length?

Thanks to all in advance!