...then that might imply the Vikings assumed the earth was round.
Why wouldn’t they? They were a sea faring people, and the round earth would be obvious to them.
Well, that's what I thought. But it wasn't until 1492 and later, even, that the world was thought, by Europeans, to be flat.
Looks like the Vikings, as long-distance sea travelers in general, had based their navigational procedures upon the assumption of sailing a globe-shaped surface. I should read more about this, since I'm studying for my Captain's license, and navigation is a big part of that.