metropolis vs municipal center

metropolis and municipal center both are nouns.

Word	Noun	Adjective	Verb	Adverb
metropolis	Yes	No	No	No
municipal center	Yes	No	No	No

metropolis (noun)	municipal center (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