While ambling around in the hope of finding a 14th century map of Europe, I happened upon this site It’s interesting, and includes an anecdote (modern) of the ruse used by a US cartographer of adding fake towns to his maps, to catch out forgers. Someone wasn’t caught out by this, he was actually enterprising enough to set up the Agloe General Store where the map said there was a town called Agloe. Thus he created Agloe as fact!
Whether this went on in medieval times I don’t know, but nothing would surprise me. They were as wily back then as folk are now.
I still haven’t found a found a map to suit my particular purposes (for someone who is about to travel extensively from England through a number of countries and then back again in a large loop). Maybe such a thing doesn’t exist, but the above site is worth a look.
Hmm, are we sure that illustration isn’t Westeros and the Seven Kingdoms? 😉