1. a line on a map connecting points of equal magnetic declination
Usage: technical; geography; navigation

Examples

• Navigators use isogones on nautical charts to account for the difference between true north and magnetic north.
• The isogone running through this region indicates a magnetic declination of 5 degrees west.
• Isogones shift gradually over time as Earth's magnetic field changes.
• On the map, isogones are drawn as curved lines connecting areas with the same magnetic variation.