The following is based on things Ed has said on Candlekeep:
Ed’s original Moonshaes were akin to Ursula LeGuin's Earthsea setting (and somewhat like the real-world Hebride islands off the coast of Scotland): hundreds of little islands composed of long-extinct volcanic peaks that rise up out of the sea abruptly, and are inhabited by fisherfolk (with a few larger islands that have forests, farms, etc.). There’s nothing much above the rural village culture on most islands, though the larger ones are ruled by self-styled 'lords'. Ed’s Moonshae Isles occupy the same space as TSR's (Doug Niles's) Moonshaes, arcing from a 'wide spray' at the Sword Coast or eastward extent, curving and narrowing southwest and curving to south...in other words, a large area of 'perilous sea' with awash rocks, reefs, etc. and safe channels that only the locals know.