There are Four types of Pirate Maps unless you count the other piece unwriten that you can drop on the Pirate Bosses.
Treasure Map (Pirate)
( Loot : Pirate Buccaneer, Pirate Cutthroat, Pirate Marauder). This item is used to access the Treasure island holes, and by using it , it will disapear.)
This one can be used to check crustacea.
Treasure Map (Fake)
( Only can be bought from NPC John on Treasure island , and after using 100 of them you get the achievement ''Slim Chance'', note that it is only possible to get the achievement with this one. )
Pirate Treasure Map
( This Item is obtained in the Treasure Hunt Quest, and it can be used to sail to the Treasure Hunt Island )
(This item looks like the ones above, and it is studied during the Meriana Quest )
Very Old Piece of Paper
(Item dropped on the Pirate Bosses, and it's a item necessary for the beginning of the Treasure Hunt Quest )