urban center vs Saigon

urban center and Saigon both are nouns.

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

urban center (noun)	Saigon (noun)
a large and densely populated urban area; may include several independent administrative districts	a city in South Vietnam; formerly (as Saigon) it was the capital of French Indochina