agonic line

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agonic line

[ā′gän·ik līn]
(geophysics)
The imaginary line through all points on the earth's surface at which the magnetic declination is zero; that is, the locus of all points at which magnetic north and true north coincide.

agonic line

agonic lineclick for a larger image
A line drawn on a map or chart joining places of zero magnetic variation. The agonic line is a particular case of an isogonic line.