urban center vs Karachi

urban center and Karachi both are nouns.

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

urban center (noun)	Karachi (noun)
a large and densely populated urban area; may include several independent administrative districts	the largest city in Pakistan; located in southeastern Pakistan; an industrial center and seaport on the Arabian Sea; former capital of Pakistan