metropolis vs down town

metropolis and down town both are nouns.

Word	Noun	Adjective	Verb	Adverb
metropolis	Yes	No	No	No
down town	Yes	No	No	No

metropolis (noun)	down town (noun)
people living in a large densely populated municipality	the center of a city
a large and densely populated urban area; may include several independent administrative districts