isogonic line vs isogonal line

isogonic line and isogonal line both are nouns.

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

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

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

Other synonyms of isogonic line include isogone.

isogonic line (noun)	isogonal 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