This page will have a guide to the treasure map you find in Andreas Island in Assassin's Creed IV Black Flag
Treasure Map Location[edit]
The treasure map itself can be found in a Cadaver in the southern shore of the island:
Andreas Island is located at coordinates (579,720)
Treasure Map Tool[edit]
This is the treasure map you find:
Coordinates indicate (606,835)
Note that the treasure chest itself is NOT located on Andreas Island (where you got the treasure map from), but rather on an island called Abaco Island at the coordinates listed on the map, (606,835)
Dig Site Location[edit]
Sail to Abaco Island (You might have it available for fast travel if you unlocked the viewpoint when you visited there in sequence 3)
Set the marker to the mini-island across from the northeast shore:
Head towards these trees:
Walk around the base of those trees until the option to dig appears. See below for exact location:
Dig the treasure out you should get 4,000 Reales: