urban center vs Omsk

urban center and Omsk both are nouns.

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

urban center (noun)	Omsk (noun)
a large and densely populated urban area; may include several independent administrative districts	a city in the Asian part of Russia, Russia's seventh-largest city