Portsmouth vs urban center

Portsmouth and urban center both are nouns.

Word	Noun	Adjective	Verb	Adverb
Portsmouth	Yes	No	No	No
urban center	Yes	No	No	No

Portsmouth (noun)	urban center (noun)
a port town in southeastern New Hampshire on the Atlantic Ocean	a large and densely populated urban area; may include several independent administrative districts
a port city in southern England on the English Channel; Britain's major naval base
a port city in southeastern Virginia on the Elizabeth River opposite Norfolk; naval base; shipyards