San Diego vs urban center

San Diego and urban center both are nouns.

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

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