What is an isogonic line?

An isogonic line is defined as a line on a map that connects points of equal magnetic variation. Magnetic variation, also known as magnetic declination, refers to the angle difference between true north (geographic north) and magnetic north (the direction a magnetic compass points). These lines are important for navigation, especially in aviation, as they help pilots understand how much their compass reading may differ from true north due to local variations in the Earth's magnetic field.

Understanding the significance of isogonic lines is crucial for ensuring accurate navigation, as failure to account for magnetic variation can lead to navigational errors. It is important for pilots to be aware of these variations in their flying area, which is why maps used for navigation often include isogonic lines to convey this information.

The other options relate to different geographic or atmospheric phenomena and do not pertain to magnetic variation. For example, lines of equal temperature relate to climatic conditions, lines marking atmospheric pressure are involved in weather patterns, and lines representing wind direction concern meteorological data.