City of the Angels vs urban center

City of the Angels and urban center both are nouns.

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

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