What is an isogonal?

An isogonal is specifically defined as a line that connects points of equal magnetic variation on a map or a chart. Magnetic variation, also known as magnetic declination, represents the angle between magnetic north (the direction a compass points) and true north (the direction along the Earth's surface toward the geographic North Pole). This concept is crucial for navigation, as it helps pilots and navigators adjust their compass readings to ensure accuracy in directional orientation.

By following the isogonals on a chart, one can make necessary corrections to account for the variation in magnetic declination in different geographical locations. Understanding this enables more precise navigation, especially when flying in areas where magnetic variations are significant.

The other concepts, while related to navigation or meteorology, do not define an isogonal. Lines of equal speed pertain to wind patterns, lines connecting air masses refer to fronts, and altitude corrections deal with altimeter settings but do not involve magnetic variation.