Meaning of isogonic in English:

isogonic

Pronunciation /ˌʌɪsə(ʊ)ˈɡɒnɪk/

adjective

(also US isogonal)
Geography
  • Indicating or connecting points of the earth's surface at which the magnetic declination is the same.

    • ‘By 1701 Edmond Halley had dashed these hopes, showing that in the western North Atlantic, for instance, the isogonic lines (of constant variation) run almost east-west and so are independent of longitude.’

Origin

Mid 19th century from Greek isogōnios ‘equiangular’ + -ic.