city vs Johannesburg

city and Johannesburg both are nouns.

Word	Noun	Adjective	Verb	Adverb
city	Yes	No	No	No
Johannesburg	Yes	No	No	No

city (noun)	Johannesburg (noun)
people living in a large densely populated municipality	city in the northeastern part of South Africa near Pretoria; commercial center for diamond and gold industries
a large and densely populated urban area; may include several independent administrative districts
an incorporated administrative district established by state charter