Sao Paulo vs city

Sao Paulo and city both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sao Paulo	Yes	No	No	No
city	Yes	No	No	No

Sao Paulo (noun)	city (noun)
an ultramodern city in southeastern Brazil; the largest city in South America	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts
	an incorporated administrative district established by state charter