Final answer:
Magnetic bearing is important to use on topographic maps because it accounts for magnetic declination, which can vary depending on location and year the map was made. By using magnetic bearing, you can obtain accurate directions by adjusting for magnetic declination. Using true bearing without accounting for magnetic declination can lead to inaccurate directions.
Step-by-step explanation:
When determining direction on topographic maps, it is important to use magnetic bearing instead of true bearing because topographic maps typically show magnetic declination. Magnetic declination is the difference between true north and magnetic north, and it varies depending on the location and the year the map was made. By using magnetic bearing, which takes into account the magnetic declination, you can obtain more accurate directions when navigating with a compass.
For example, let's say you're using a topographic map that was made in 2000 and the magnetic declination for that area in 2000 is 8 degrees west. If you were to use the true bearing, it would not account for the magnetic declination and your directions would be inaccurate. However, by using the magnetic bearing, you can adjust for the 8 degrees west declination and obtain the correct direction.
Using magnetic bearing instead of true bearing ensures that you are taking into account the Earth's magnetic field and the variation in magnetic declination, resulting in more precise navigation on topographic maps.