Tethis (a sea troll) tells us about the Circumfence in The Colour of Magic. It's not small.
“It could be extended for a couple of miles, if you found enough rocks and things,” said the wizard.
“Ten thousands of miles. I just patrol this league.”
“That’s a third of the way around the Disc!”
You can see it on the authorised Discworld Mappe. Not quite a ...
French Wikipedia has an interesting, although unsourced, hypothesis. Périgord department, where the author lived. Now known as Dordogne department. Many locations in the novel are strangely reminiscent of local landmarks.
L'action se situe dans le Périgord, où vit l'auteur. Les lieux cités font étrangement penser à des lieux existants. Ainsi Malevil ...