San Juan vs metropolis

San Juan and metropolis both are nouns.

Word	Noun	Adjective	Verb	Adverb
San Juan	Yes	No	No	No
metropolis	Yes	No	No	No

San Juan (noun)	metropolis (noun)
the capital and largest city of Puerto Rico	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts