Marinas don't headline trailers, but they're consistently some of the most frequented areas on any GTA 6 map. Trailer 2 features marina frames - calm, affluent stretches by the water with yachts moored and smaller boats moving in and out.
This article is about the marina districts within Vice City. For the industrial waterfront, see the port district piece.
What the marina frames show
Yachts. Small pleasure boats - cruisers, sport-fishing boats. Jet-skis pulled up on trailers, jet-skis out on the water. A wooden boardwalk running along the seawall. Palms, restaurant frontage, the kind of waterfront that sits between the strip and the residential beach blocks.
Visual coding is play, not work. It's unlike the port district in terms of lighting, density and architecture.
Where the marinas sit relative to the rest of Vice City
Plural - likely multiple. Trailer aerials suggest a marina near downtown on the mainland side, as well as shoreline mooring on the barrier island near the art deco strip. The upscale mansion districts likely have private docks nearby as well.
The marinas probably stretch beyond the city proper as well - the bridge route to the Keys has to start somewhere, and a southern marina would fit near that transition.
What marinas are likely to be used for
Acquiring boats. Side-content fishing or smuggling (speculative, based on history). Boat-based story missions. Photo spots. Leisurely cruising along the coast. Likely the starting point for some of the boat routes around the wider coastline.
Historical comparison: GTA V had marinas which handled boat activities - mostly side content, plus one or two main story missions. Wealthier marinas also provided access to expensive high-end vehicles. The same pattern could plausibly work here, scaled up for a more boat-heavy map.