isogonal line vs isogonic line

isogonal line and isogonic line both are nouns.

Word	Noun	Adjective	Verb	Adverb
isogonal line	Yes	No	No	No
isogonic line	Yes	No	No	No

As nouns, isogonal line and isogonic line are synonyms defined as:

isogonal line and isogonic line: an imaginary line connecting points on the Earth's surface where the magnetic declination is the same

Other synonyms of isogonal line include isogone.

isogonal line (noun)	isogonic line (noun)
an imaginary line connecting points on the Earth's surface where the magnetic declination is the same	an imaginary line connecting points on the Earth's surface where the magnetic declination is the same