urban center vs Rio

urban center and Rio both are nouns.

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

urban center (noun)	Rio (noun)
a large and densely populated urban area; may include several independent administrative districts	the former capital and 2nd largest city of Brazil; chief Brazilian port; famous as a tourist attraction