A long time ago, a band of adventurers carved a few markings onto a table while they drank and planned their next expedition.
Over time, it grew and grew and eventually encompassed the whole table as more and more adventurers added details to it.
Sadly, the original table was destroyed in a bar fight, rendering the only map of the West Marches lost to the sands of time.
Now, only this painting remains of the original table (embellished, of course; the original was made of knife carvings) and even then, it wasn't as detailed as the original nor as expansive, only covering the area around Fidem.
Still, for aspiring adventurers, its better than nothing.