North is shown on the bottom of a topographic map by three arrows whose tips are marked MN, , GN. These refer to Magnetic North, True North, and Grid North, respectively.
Usually, True North is toward the top of the map; it is defined by the meridians of longitude.
Magnetic North is the direction toward which a compass needle points within the map area. The angle between Magnetic North and True North is known as magnetic declination. Because the magnetic pole shifts westward with time, the declination needs to be monitored and updated for accurate navigation.
Measuring Bearings
Grid North shows the difference between the rectangular grid on the map and True North. This difference happens because a map is a flat illustration of the Earth's curved surface.
True North is different from Magnetic North because the Earth's geographic North Pole and its magnetic North Pole are not located at the same place. The angle between them (magnetic declination) changes as you move to different places on the globe. For compass bearings to be the same as bearings measured from a map, the compass must be set to make up for magnetic declination. If you didn't, your map and compass bearings would be measured from different 0° (north) lines. What then? You'd be lost! A True North map bearing can be converted to a Magnetic North compass bearing, or the other way around, by either adding or subtracting the value of the magnetic declination the value of True North.
Directions are shown in degrees as either bearings or azimuths. A bearing measures the degrees of an angle, east or west, from north or south from zero to a maximum of 180 degrees. Azimuths are similar to bearings, but degrees are counted clockwise for 360 degrees, beginning and ending at north.
Measuring Azimuth
Hands on Activity
Try out the Measuring Bearing hands-on activity. You will need to have Adobe Acrobat Reader installed on your computer to view and print the activity and answer sheets. If you do not have Acrobat Reader installed click the "Get Acrobat Reader" icon below. Have fun!
, GN. These refer to Magnetic North, True North, and Grid North, respectively.
