This page will have a guide to the treasure map you find in Misteriosa in Assassin's Creed IV Black Flag
Treasure Map Location[edit]
The treasure map itself can be found on a cadaver in Misteriosa, at coordinates (303,199):
Treasure Map Tool[edit]
This is the treasure map you find:
Coordinates indicate (623,172).
Note that the treasure chest itself is NOT located in Misteriosa (where you got the treasure map from), but rather in Kingston:
Dig Site Location[edit]
Set a custom marker here:
Dig site is near a wrecked ships's hull, between some crates:
Reward is 3,000 Reales and design plans for the Blackwood Wheel