isogriv
/ˈaɪsəˌɡrɪv/
noun
- A line on a map connecting points of equal magnetic variation (the difference between true north and magnetic north).
- When planning the flight path, the navigator checked the isogriv for the region.
- The isogriv on the chart showed where the magnetic declination was the same.
- Pilots use an isogriv to adjust their compass readings for accurate navigation.