urban center vs Rostov na Donu

urban center and Rostov na Donu both are nouns.

Word	Noun	Adjective	Verb	Adverb
urban center	Yes	No	No	No
Rostov na Donu	Yes	No	No	No

urban center (noun)	Rostov na Donu (noun)
a large and densely populated urban area; may include several independent administrative districts	a seaport on the Don River near the Sea of Azov in the European part of Russia