Isogonic lines

from The Collaborative International Dictionary of English v.0.48

Isogonic \I`so*gon"ic\, a. [Iso- + Gr. gwni`a angle.]
   Pertaining to, or noting, equal angles.
   [1913 Webster]

   {Isogonic lines} (Magnetism), lines traced on the surface of
      the globe, or upon a chart, connecting places at which the
      deviation of the magnetic needle from the meridian or true
      north is the same.
      [1913 Webster]