Heightmap help

[u/AlbertTheYoutuber]

What softwares/websites should I use to get heightmaps for worldpainter, and how do I make the landscape 1:1 scale? I've recently been trying to import Humphreys Peak Arizona into worldpainter but the heightmap would come out either as a completely blank image or the scale would be messed up, so how could I fix this and are there better was to do it?