urban center vs Pittsburgh of the South

urban center and Pittsburgh of the South both are nouns.

Word	Noun	Adjective	Verb	Adverb
urban center	Yes	No	No	No
Pittsburgh of the South	Yes	No	No	No

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