In the published things Howard did describe the layout and history in broad strokesSeriously: started with the Lord of the Rings (other original sources like Howard didn't bother with a map), and everyone went from there because it's fun to draw maps for a lot of people. The left-justified fantasy map trope starts because of the European origins, but people have pointed out Greyhawk looks kind of like the Upper Midwest.
Is there a Howard-canon map of Conan's world?
And apparently had a sketch for his own use ("secret DM info"?):
Certainly more than a bit European inspired.