The Leonida Keys are the tropical islands on the map. Jason ends up here after the army and works for local smugglers. Brian Heder runs a boatyard there and rents Jason a place.
The bridges, the shallow sea, and the boats show up in trailers and on the edition list: the Shitzu Squalo and the kayak belong to water you can reach from this coast and from Vice City.
Rockstar's description is titled 'Gateway to Paradise.' Life in this tropical archipelago 'isn't flashy but it's easy,' and it sits right on the doorstep of some of the most beautiful and dangerous waters in America.
Trailer 2 places Jason's apartment in the Keys: the property Brian Heder lets him use rent-free in exchange for help with local shakedowns. Schematic fan maps also put Brian's boatyard here.
See where the regions sit on the schematic GTA 6 map.