NGA vs government agency

NGA and government agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
NGA	Yes	No	No	No
government agency	Yes	No	No	No

As nouns, government agency is a hypernym of NGA; that is, government agency is a word with a broader meaning than NGA:

NGA: a combat support agency that provides geographic intelligence in support of national security
government agency: an administrative unit of government

Other hypernyms of NGA include agency, authority, bureau, federal agency, office.

NGA (noun)	government agency (noun)
a combat support agency that provides geographic intelligence in support of national security	an administrative unit of government