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