What is a World City?

This week the New York times posted a posthumous article from late author, essayist and professor Tony Judt and his love for New York City. Here are some excerpts from the article:

But just what is a “world city”? Mexico City, at 18 million people, or São Paulo at near that, are unmanageable urban sprawls; they are not “world cities.” Conversely, Paris — whose central districts have never exceeded three million inhabitants — was the capital of the 19th century.

Is it a function of the number of visitors? In that case, Orlando, Fla., would be a great metropolis. Being the capital of a country guarantees nothing: think of Madrid or Washington (the Brasília of its time). It may not even be a matter of wealth: within the foreseeable future Shanghai (14 million people) will surely be among the richest places on earth; Singapore already is. Will they be “world cities”?

Judt continues on to state later:

And yet, New York remains a world city. It is not the great American city — that will always be Chicago. New York sits at the edge: like Istanbul or Mumbai, it has a distinctive appeal that lies precisely in its cantankerous relationship to the metropolitan territory beyond. It looks outward, and is thus attractive to people who would not feel comfortable further inland. It has never been American in the way that Paris is French: New York has always been about something else as well.