urban center vs City of the Angels

urban center and City of the Angels both are nouns.

Word	Noun	Adjective	Verb	Adverb
urban center	Yes	No	No	No
City of the Angels	Yes	No	No	No

urban center (noun)	City of the Angels (noun)
a large and densely populated urban area; may include several independent administrative districts	a city in southern California; motion picture capital of the world; most populous city of California and second largest in the United States