The aptly named DDO explorer areas use fog of war. On top of this, there will be anywhere from 15-40 "explorer" locations that reward you with a narrarated back story and xp of the location you have found. Some are easy to find, some are incredibly difficult. Along with these landmark areas, rare boss spawns may sometimes appear in these locations with chests and occasional awesome static loot. It is an excellent system.
Concerning the map, It has its fog of war style system, where the player has a 10 yard or so bubble of map revealing, and when a quest entrance or npc or something gets within that bubble, you can see it. However, if any entrance is an explorer point, you don't get it on the map until you're right ontop of it to get its XP and narrarated message.