Isogonic lines are used in navigation to indicate which variable?

Isogonic lines are used in navigation to indicate which variable?

• A. Wind speed
• B. Magnetic variation
• C. Pressure
• D. Temperature

Answer: (B)

Isogonic lines show magnetic variation, the angular difference between true north (geographic north) and magnetic north at a location. Each line connects points where this difference is the same, typically written in degrees East or West. Knowing the variation lets you adjust compass readings to obtain true headings, which is essential for accurate navigation because the magnetic field isn’t aligned with the true north everywhere and it changes with position (and over time). The other options don’t fit because wind speed, pressure, and temperature are not described by isogonic lines; those relate to weather or atmospheric conditions, not the difference between true and magnetic north.

Isogonic lines show magnetic variation, the angular difference between true north (geographic north) and magnetic north at a location. Each line connects points where this difference is the same, typically written in degrees East or West. Knowing the variation lets you adjust compass readings to obtain true headings, which is essential for accurate navigation because the magnetic field isn’t aligned with the true north everywhere and it changes with position (and over time). The other options don’t fit because wind speed, pressure, and temperature are not described by isogonic lines; those relate to weather or atmospheric conditions, not the difference between true and magnetic north.