urban center vs Aachen

urban center and Aachen both are nouns.

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

urban center (noun)	Aachen (noun)
a large and densely populated urban area; may include several independent administrative districts	a city in western Germany near the Dutch and Belgian borders; formerly it was Charlemagne's northern capital