Rockstar always makes up names for places. Vice City is fictional but Miami-coded; Leonida is fictional but Florida-coded. This page is a work-in-progress index of which fictional names show up in official Rockstar material and what they likely represent in the real world.
Cautiously hedged. Several names that have been mentioned in community discussion have not been substantiated by any official release; we do not list them as fact.
Confirmed in official material
Leonida (state). Vice City (biggest city). These are the names Rockstar has used in Newswire posts and trailer copy.
This page will be updated with any other named locations that have been seen on screen or mentioned in official posts by the time you are reading this. As of this writing, there are not many.
Names from community discussion
Port Gellhorn, Ambrosia, Grass Rivers, Mount Kalaga - these names pop up in community trailer breakdowns and freeze-frames. They may be on-screen; some have been definitively seen in trailer text. Every name should be checked against the source before being considered confirmed.
If we can confirm that a name appears in a trailer, we consider it confirmed. If the name has spread via the community but we can't find where it came from, we are unsure.
Plausible real-world correspondences
Vice City → Miami. The Keys analogue → Florida Keys. The wetland region → Everglades / Big Cypress. Inland small towns → various towns from central Florida.
Town-to-town mappings should be considered loose inspiration rather than 1:1 matches.