Using a Military Protractor on a Topo Map

THE AMERICAN BACKPACKER

Land Navigation is a topic I enjoy teaching.  Understanding the basics of Land Navigation will make your wilderness adventure enjoyable and more importantly safe.  This lesson will discuss how to use a military protractor on a topographical to get an azimuth/bearing.  A protractor is an instrument used to help you measure angles (360 degrees) on a map.  Protractors come in different shapes.  The more popular shapes are:  

PROTRACTOR TYPES:

  • Circle
  • Semi-Circle
  • Square
  • Rectangle

In this lesson, I will be using a square (military) protractor which I learned to use in the Army.  This protractor has the following features:

FEATURES:

  • Mils Scale (6400 mils 1 mil = 17.8 degrees)
  • Degrees Scale (360 degrees)
  • Index Point (Center point of the protractor where the baseline and horizontal line crosses).
  • Baseline
  • Grid Coordinate Scale (1/50000, 1/100000, 1/25000, 1/250000)
Military Protractor
Components of a Military Protractor

USING THE PROTRACTOR:

In this lesson, we will be using 2 components of the above protractor. The (360) degrees scale and the index point.  The other components will be discussed later in another lesson. Some individuals cut away the mils portion of the protractor because it is rarely used for land navigation.  Units in the military such as the artillery will use the mils scale for accuracy.  Below is a picture of a protractor that has a cut away mils scale.  The below protractor also has duct tape around its border.  The reason you may want to put tape on the back of a protractor is because the black lettering on a protractor blends in with many topo maps. The tape allows for more contrast and it allows you to see the black degree tick marks we will use to get the azimuth.  I used gray duct tape but any dark colored tape will work.

Protractor with Mils scale cut away and tape on back for contrast

  1. Find a point on a map that you will begin from when plotting an azimuth. In the below map lets say we are starting from (hilltop #1).
  2. Next find your destination point. In the below map our destination point will be (hilltop #2) .
  3. Draw a line from your starting point, (hilltop #1), to your destination point, (hilltop #2). Use a pencil so you can erase afterwards.

Starting point #1 (Hilltop) to ending point #2 (Hilltop)

Place your index point on your protractor on hilltop #1.  Make sure that the baseline is parallel to a nearest grid line on your map. There are many grid lines on a map to choose from so use the one nearest to your starting point, (hilltop #1). 

Military Protractor

Topo Map Grid Lines to use when signing up your Protractor

Follow the line you drew from your index point to the degrees scale.  The azimuth is 327 degrees.  This is your map grid azimuth from hilltop #1 to hilltop #2.  Now you are ready to convert this grid azimuth over to a magnetic azimuth on your compass.  If you use a compass such as the Suunto MC-2G compass you can set the compass to the magnetic declination of your topo map so no conversion is necessar. If you need to convert the grid azimuth because you do not have this feature on your compass then go to this article I wrote on how to do so, Magnetic Declination

Protractor Azimuth

327 Degree Grid/Map Azimuth

CONCLUSION:

Basic land navigation is becoming a lost skill.  This skill is being forgotten because of modern day technology, (GPS units), which we all use in the wilderness.  I always carry a GPS with me and you should to.  Understanding basic land navigational skills will allow you to navigate a wilderness area if this technology goes down or you run out of battery power.  I have a section on different land navigational topics/skills here on my website under Backpacking Blog: Land Navigation, for your review.

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