Triforce Chart
Triforce Charts are purple maps found only in The Wind Waker and are necessary to finish the game. The Triforce of Courage has been split up into eight shards, and Link must collect all the shards to help form the Triforce and return to Hyrule. Each Triforce Chart shows the location of the shard, but once Link obtains one, it proves to be unreadable. Link must take the charts to Tingle, who will decipher them for 398 Rupees each and make them readable to Link. Once Link has allowed Tingle to decipher all eight charts, it will come to a total of 3184 Rupees.
Locations
Triforce Charts are relatively hard to find, and require skill and cleverness to actually obtain them. They are scattered throughout the Great Sea, and they are hidden usually in secret caves. For a full detailed walkthrough of where to find the shards and the maps, look at this site's walkthrough section at this link.