On my Arden Campaign map I used the "known" World of the empire, from which most playercharacters and the most sophisticated cartographers of my world come from, It have roughly the size of Scandinavia to Northafrica for scale. Dont overdo your details exept it is a merchant trading/ Pirate / Wiking kind of map than concentrate on important capitols and coast cities and ports, try to imagine what the natural, cultural and travelable borders of the area your group inhabit. If it is a world tournee and they visit another continent every day you play... well, lots of maps to do.