"Then, another consideration comes to my mind: in a traditional medieval age, most people are ignorant and superstitous, and rarely leave, if ever, the vicinity of their native village. Then, maps of the planets are rarely available, if existing at all. So I guess, one idea would be of taking an already existing world (preferably a homebrew that no player knows about), but not show any map to the players, and not tell them anything beyond their imediate region plus vagu rumors. Then, to make the game more fun to the players, only make sure to make it fit with their preferences (i.e.: like high fantasy with elves, etc., or low-magic with humans only)."
I would LOVE a game run in this manner.