In Grand Theft Auto III, several billboards advertise vacations to Miami, and Ray Machowski mentions he is leaving for there when the CIA try to prevent his escape from Liberty City. In Grand Theft Auto: Vice City, there is a billboard in Little Haiti that says "Move over Miami", implying that even if Vice City was based in Miami, the two cities both exist in the 3D Universe, and may be roughly similar. The original GTA III website also makes clear a coexistence between Miami and Vice City:
"Francis International is airport to the stars. 100's of domestic and international destinations served including: London, San Andreas, Vice City, Miami, Bogota, Amsterdam, Bangkok, Toronto, Leith and Tokyo."