Rostov na Donu vs urban center

Rostov na Donu and urban center both are nouns.

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

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