The flagship city of GTA V vs the flagship city of GTA 6. Different real-world references, different design philosophies, different decades.
Reference cities
Los Santos = Los Angeles. Vice City = Miami. Both real cities; both heavily stylised in the game.
LA's coding is film-industry, traffic, sprawl, valley-vs-coast geography. Miami's coding is beach-tourist, art deco, latin culture, intracoastal geography. Different vibes.
Scale
LS in GTA V is famously dense in the south, sparser in the north. Vice City based on trailer footage looks dense throughout, with the suburbs continuing the density into the inland transition.
Total Vice City + Leonida is plausibly larger than LS + Blaine. Vice City alone vs LS alone is closer.
Architecture and feel
LS was modern-American-glass plus Vinewood-hills mansions plus Vespucci beach plus industrial waterfront. Vice City is art-deco strip plus Brickell-coded downtown plus Star-Island mansions plus port. Different vocabulary.
Density
Vice City visibly denser at street level. We discuss this on the density vs size piece.