noun
isogonic line; isogonal line
Technical term in geomagnetism and navigation: a line on a map connecting points of equal magnetic declination.
等偏角線は磁気偏角が等しい地点を結んだ線です。
An isogonic line is a line connecting points of equal magnetic declination.
Compound of 等 (equal), 偏角 (declination), and 線 (line), directly corresponding to the English term 'isogonic line'.