isogonies
/aɪˈsɑɡəniz/
noun
- Lines on a map connecting points where the magnetic declination (the angle between true north and magnetic north) is the same.
- The isogonies on the chart were clearly marked for navigation purposes.
- Geologists study isogonies to understand changes in Earth's magnetic field over time.
- The map showed isogonies that helped sailors adjust their compasses.