urban center vs Plovdiv

urban center and Plovdiv both are nouns.

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

urban center (noun)	Plovdiv (noun)
a large and densely populated urban area; may include several independent administrative districts	an ancient city in southern Bulgaria; commercial center of an agricultural region