Sea Chart
From Zelda Wiki.org
The Wind Waker
The Wind Waker's Sea Chart is split up into 7-by-7 sections. When Link first receives this item, it has only a small portion of the islands charted in it. It is eventually learned that giving a Fishman some All-Purpose Bait while in a section of the Sea Chart that has yet to be charted, the Fishman will mark the location of the island on the Sea Chart, along with passing on some useful information.
Phantom Hourglass
Spoiler warning: If you have not completed the relevant game(s), then the following details could spoil your experience.
In Phantom Hourglass, the Sea Chart is much smaller, being split into four sections with several islands each. Link uses the Sea Chart to find the Ghost Ship and rescue Tetra. Eventually Link was able to find all four parts of the Sea Charts located inside the Temple of the Ocean King. Islands are charted differently in this game, with most of the islands already displayed on the Chart upon obtaining that section. There are, however, uncharted islands which automatically become charted upon visiting them.
Bizarrely, the Sea Charts in Phantom Hourglass take on the same appearance of the Treasure Charts in The Wind Waker, despite being a direct sequel to the game.
