urban center vs San Diego

urban center and San Diego both are nouns.

Word	Noun	Adjective	Verb	Adverb
urban center	Yes	No	No	No
San Diego	Yes	No	No	No

urban center (noun)	San Diego (noun)
a large and densely populated urban area; may include several independent administrative districts	a picturesque city of southern California on San Diego Bay near the Mexican border; site of an important naval base