What term describes the line that connects points of zero variation where only one exists?

The term that describes the line connecting points of zero variation is "Agonic." The agonic line represents locations on the Earth's surface where magnetic north aligns exactly with true north, meaning there is no magnetic declination or variation at those points. This is significant for navigation because it indicates regions where magnetic compasses do not need to be adjusted for declination.

In contrast, the isogonic line refers to lines of equal magnetic variation, which denotes areas where the angle of declination is consistent but not zero. Deviation pertains specifically to errors in magnetic compass readings due to local magnetic influences, while the term magnetic relates broadly to the Earth's magnetic field but does not specifically describe the concept of zero variation.

Understanding the distinction between the agonic line and these other terms is crucial for effective navigation, as it allows pilots and navigators to accurately interpret compass readings in relation to true geographic orientation.