Bearings: (sometimes also referred to as azimuths):

Angle Terminology (Bearings):

You may come across several terms used to describe angles in navigation. I will use 'Bearing' exclusively in this text. If no clarification is given a bearing is a line of direction with an angle measured clockwise in degrees from Magnetic North.

However if specified as a True Bearing it is referenced clockwise from True North, and if specified as a Grid Bearing it is referenced clockwise from Grid North (on a particular map).

A similar term called an Azimuth is by default an angle measured clockwise from True North, unless it is specified as a Magnetic Azimuth - referenced to Magnetic North or a Grid Azimuth - referenced to Grid North (on a particular map).

You may also hear the term Traverse - which is a straight line used in triangulation for surveying or position location it has no particular default reference point.

I will use only Grid Bearing or Magnetic Bearing - they are sufficient for all normal descriptive purposes. It is technically redundant to use Magnetic Bearing but I think it adds clarity. I see no particular value in referencing to True North for typical outdoor navigation purposes.

So:

Magnetic Bearings (same as magnetic azimuths) are bearings determined using a compass from magnetic north.

Grid Bearings (same as grid azimuths) are bearings determined using a protractor from grid north on a map (note you may also use a base plate compass as a protractor to measure this).

Converting a given Bearing between Magnetic (Compass) to Grid (Map) requires you compensate for the Grid-Magnetic Angle.

A square map protractor with a 360 degree scale like this is easier to use and align to a map grid than a circular protractor.

It also includes UTM grid scales (the triangles) these are designed for accurately locating positions within map grids of different scale maps.

Military versions may have graduations in Mils in addition to degrees (like on this one)

Some have a thin string from the mid point (index) so you can measure bearings to points across the map without a ruler 

A back bearing (back azimuth) is the angle needed to travel in the reverse direction from a normal bearing (think return trip!). Calculate a back bearing by adding 180 degrees and subtracting 360 degrees only if the resulting angle is more than 360 degrees, (can be either grid or magnetic depending on source).

Cross-bearings are a pair (or more) of bearings from known positions that are used to establish a specific location where they intersect, often used to locate your actual current position using a map and compass, (can be either grid or magnetic depending on source).

ACM 1/2007
 

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