The Grid Magnetic (GM) Angle is used to

The Grid Magnetic (GM) Angle is used to

• A. Convert magnetic azimuth to grid azimuth and vice versa
• B. Set the map scale
• C. Determine contour interval
• D. Identify legend symbols

Answer: (A)

The Grid Magnetic angle represents the difference between grid north and magnetic north on a map, and it is used to convert between magnetic azimuths (what you measure with a compass) and grid azimuths (the bearing used on the map). If the magnetic north is east of grid north, you add the GM angle to a magnetic bearing to get the grid bearing; if magnetic north is west, you subtract it. For example, with a GM angle of 10 degrees east, a magnetic bearing of 055 degrees becomes a grid bearing of 065 degrees. If you reverse the process, a grid bearing of 065 degrees corresponds to a magnetic bearing of 055 degrees. This conversion is what the GM angle is for, and it isn’t used to set map scale, determine contour intervals, or identify legend symbols.

The Grid Magnetic angle represents the difference between grid north and magnetic north on a map, and it is used to convert between magnetic azimuths (what you measure with a compass) and grid azimuths (the bearing used on the map). If the magnetic north is east of grid north, you add the GM angle to a magnetic bearing to get the grid bearing; if magnetic north is west, you subtract it. For example, with a GM angle of 10 degrees east, a magnetic bearing of 055 degrees becomes a grid bearing of 065 degrees. If you reverse the process, a grid bearing of 065 degrees corresponds to a magnetic bearing of 055 degrees. This conversion is what the GM angle is for, and it isn’t used to set map scale, determine contour intervals, or identify legend symbols.