Sioux City vs urban center

Sioux City and urban center both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sioux City	Yes	No	No	No
urban center	Yes	No	No	No

Sioux City (noun)	urban center (noun)
a city in northeastern Iowa where the Big Sioux River joins the Missouri	a large and densely populated urban area; may include several independent administrative districts