Leonida is Rockstar's Florida. Six regions have been confirmed, and between them they cover everything the trailers and the Extended Look have shown.
Why the regions matter
GTA V's map was one city and its hinterland. Leonida is a whole state. A dense modern Vice City at the bottom of the east coast, an island chain trailing off the south, wetlands in the middle, farm and industrial country inland, a working port in the northwest and forested highlands in the north. The story opens in the Keys, at Jason's house, and the world expands from there as the chapters progress.
Nobody knows how big it is
Rockstar has never published a figure, and the numbers circulating are not reconcilable with each other. Three times Red Dead Redemption 2's playable area, twice GTA V, seventy per cent bigger than GTA V from the 2022 leak map, Vice City alone at twice Los Santos. Several of those come from the same reveal and still disagree.
What is safe to say is that it is a state rather than a city, it covers six named regions, and it is comfortably the largest map Rockstar has built. The pause-menu map is satellite imagery with fog-of-war, so you fill it in yourself.
A warning about district names
You will find long lists of Leonida counties and Vice City neighbourhoods elsewhere. Some come from signage in official footage, most come from community mapping or the 2022 leak, and sources actively disagree about which is which. Rockstar has confirmed six regions. Everything beyond that is someone's reading of a freeze-frame.