Ok let's see...
-GTA: Liberty City (New York City), San Andreas (San Francisco), and Vice City (Miami).
-GTA London: London.
-GTA2: Anywhere City (?).
-GTA III: Liberty City (New York City).
-GTA VC: Vice City (Miami).
-GTA SA: San Andreas (San Francisco).
-GTA IV: ...
It could be either London again, or Anywhere City, which could be, for exampl... Liberty City set in the future!
But i doubt it'll be just one city. So LibertyCity doesn't fit. Maybe it could be LC and AC and London heh.