Leningrad vs urban center

Leningrad and urban center both are nouns.

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

Leningrad (noun)	urban center (noun)
a city in the European part of Russia; 2nd largest Russian city; located at the head of the Gulf of Finland; former capital of Russia	a large and densely populated urban area; may include several independent administrative districts