So... where is your giant turtle???
Nice height map!

Well actually I think that in the diskworld , the concept of north is rather inconsistent. The distance from the center is not. But the diskworld is an humoristic setting so physic is not a big concern. I don't remember how the sun rise and set in that universe, was it the movement of Alduin? You might need to think about that and other related things before players start asking silly questions like the one about the earthquakes .

I do have one concern, about your map elements overlapping. For example, the mountains are transparent where there is the river so we see blue where it's supposed to be brown.