isogonals
/ˌaɪsəˈɡoʊnəlz/
noun
- Lines on a map or chart connecting points where the magnetic declination (the angle between true north and magnetic north) is the same.
- The meteorologist studied the isogonals to predict navigation conditions.
- Hikers used isogonals to understand local magnetic variations.
- The map showed isogonals to help sailors adjust their compasses.