isogonic line


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isogonic line

[′ī·sə¦gän·ik ‚līn]
(geophysics)
Any of the lines on a chart or map showing the same direction of the wind vector.
Any of the lines on a chart or map connecting points of equal magnetic variation.

isogonal

isogonalclick for a larger image
A line drawn on a map or a chart joining points of equal variation (magnetic declination). On aeronautical charts, isogonic lines appear as irregular dashed lines (−3° E), and their values also are indicated alongside the lines. The annual change in their values is indicated at the bottom of the chart. Also called an isogonic line.