Riga vs national capital

Riga and national capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Riga	Yes	No	No	No
national capital	Yes	No	No	No

Riga (noun)	national capital (noun)
a port city on the Gulf of Riga that is the capital and largest city of Latvia; formerly a member of the Hanseatic League	the capital city of a nation