How do magnetic meridians differ from geographic meridians?

Magnetic meridians differ from geographic meridians primarily in that they can vary with time and location. The geographic meridian, which is aligned with the Earth’s rotational axis, remains relatively constant, representing the true north direction. In contrast, magnetic meridians are determined by the Earth's magnetic field, which is subject to changes due to factors like geological activity and solar influences. This variability means that a magnetic meridian can differ based on where you are on the Earth and can also change over time, making them less stable compared to geographic meridians.

Understanding this distinction is crucial in surveying, as reliance on magnetic north can introduce errors if the magnetic declination (the angle between magnetic north and true north) is not correctly accounted for, especially when conducting precise measurements or mapping.