What does the term "isogonal" refer to in navigation?

The term "isogonal" specifically refers to lines that connect points of equal magnetic variation, also known as magnetic declination, across a geographical area. This concept is crucial for navigation because it helps navigators understand how the magnetic compass reading differs from true north due to local variations in the Earth's magnetic field.

By providing a visual representation of these variations, isogonal lines enable navigators to make necessary adjustments to ensure accurate course plotting and heading determinations based on magnetic compass readings. Understanding these lines is essential for safe and effective navigation, especially in regions where variations can be significant.