In the Superman FILMS - Metropolis is New York. Of course I think it is left to interpretation in other areas (TV, comics, etc.) - but in the films, most certainly Metropolis = NYC. Don't believe me? How about the Statue of Liberty and the World Trade Center making an appearance in the Reeve films (I still tear up when Supes and Lois fly by the twin towers).
So to me, Metropolis has always been NYC. Just my thoughts.
