Rostov on Don vs urban center

Rostov on Don and urban center both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rostov on Don	Yes	No	No	No
urban center	Yes	No	No	No

Rostov on Don (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