metropolis vs Pittsburgh of the South

metropolis and Pittsburgh of the South both are nouns.

Word	Noun	Adjective	Verb	Adverb
metropolis	Yes	No	No	No
Pittsburgh of the South	Yes	No	No	No

metropolis (noun)	Pittsburgh of the South (noun)
people living in a large densely populated municipality	the largest city in Alabama; located in northeastern Alabama
a large and densely populated urban area; may include several independent administrative districts