* Topographic maps show True North. The grid lines and compass rose on a topographic map are aligned with True North, which is based on the Earth's rotational axis.
* Magnetic declination varies. The difference between True North and Magnetic North, called magnetic declination, changes depending on your location and over time. It's not constant.
How to find the difference:
1. Look for a declination diagram: Most topographic maps include a small diagram that shows the magnetic declination for the area covered by the map. It usually includes a line showing the angle between True North and Magnetic North, along with the year the declination was measured.
2. Use a compass and a declination calculator: If the map doesn't have a declination diagram, you can use a compass and a declination calculator (available online) to determine the declination for your specific location and date.
Important note: Magnetic declination is constantly changing. If the map is old, the declination value may be outdated. Always use the most recent declination information for accurate navigation.
