In GTA 5, the only city will be Los Santos. According to the art director of the entire project, the map will be “bigger than the worlds of Red Dead Redemption, San Andreas, and Grand Theft Auto IV combined, with room to spare." If this claim is true, this map will be absolutely colossal.
There will be a fairly large amount of country side in the game, as well as some smaller towns and minor cities in the outskirts of Los Santos. There are also rumors that a military base will be stationed somewhere in the city, which is also why there’s such a high tech jet in the official trailer.
There are no “official” images of the GTA 5 map, so in other words the fans will have to wait until the official release in order to get a taste of the real thing. It’s unknown what it will look like but there will be the bottom of the ocean, farmlands, Los Santos, and potentially a few other minor features.
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