city vs San Diego

city and San Diego both are nouns.

Word	Noun	Adjective	Verb	Adverb
city	Yes	No	No	No
San Diego	Yes	No	No	No

city (noun)	San Diego (noun)
people living in a large densely populated municipality	a picturesque city of southern California on San Diego Bay near the Mexican border; site of an important naval base
a large and densely populated urban area; may include several independent administrative districts
an incorporated administrative district established by state charter