district line vs boundary

district line and boundary both are nouns.

Word	Noun	Adjective	Verb	Adverb
district line	Yes	No	No	No
boundary	Yes	No	No	No

As nouns, boundary is a hypernym of district line; that is, boundary is a word with a broader meaning than district line:

Other hypernyms of district line include bound, bounds.

district line (noun)	boundary (noun)
the boundary between two districts	the greatest possible degree of something
	the line or plane indicating the limit or extent of something
	a line determining the limits of an area