Ok! As per the marriam-webster definition of a metropolis:

the chief or capital city of a country, state, or region,

the city or state of origin of a colony (as of ancient Greece),

a city regarded as a center of a specified activity,

a large important city.

As per Cambridge:

a very large city, often the most important city in a large area or country.

Collins:

A metropolis is the largest, busiest, and most important city in a country or region.

Britannica:

a very large or important city — usually singular

Oxford:

A very large urban settlement usually with accompanying suburbs. No precise parameters of size or population density have been established. The structural, functional, and hierarchical evolution of global metropolises is rooted as much in the past as in the present: modern information and communications technology may be more advanced than the 19th-century telegraph, but the processes and outcomes are much the same (Daniels (2002) PHG 26). ‘[Berlin's] wealth of facilities, as well as their scatter across the metropolis, can be understood only in the light of the city's history and, paradoxically, its troubles.

Longman:

a very large city that is the most important city in a country or area

You:

NYC but only if half the people use public transit