Home: GPS Education: Triangulating Your Location

Where in the World: Triangulating Your Location

By Sid Nair

Knowing how to use a compass is a skill that will become important if you ever find yourself lost, whether in the middle of nowhere or just slightly off the beaten path. Although it's easy to depend on high-tech navigation systems in today's world, knowing how to use a magnetized compass and a paper map could be invaluable in a difficult situation. One you learn about identifying the basic parts of a compass and understanding how to set and use the compass in tandem with a map, you'll be ready to determine your location and navigate in the direction you need to go if your electronic gadgets lose power or malfunction.

Compass Anatomy

Compasses can vary in their features. You will need to have one with specific features to enable you to use it for basic navigation.

  • Baseplate: This is the bottom of the compass. Ideally, it's best to be able to see through a transparent baseplate so you can place the compass directly on a map and look through it. Look for a compass with a straight edge so you can get your bearings and transfer them to the map.
  • Ruler: The ruler will enable you to determine distances using a map scale.
  • Direction of Travel Arrow: This arrow indicates the direction to point the compass when you are gathering or following a bearing.
  • Rotating Bezel: Some call this an "azimuth ring." This is the outer circle of the compass with 360-degree markings.
  • Index Line: Find the index line right above the bezel. Some call this the "read bearing here" mark.
  • Magnetized Needle: The red end of the magnetized needle will always point toward magnetic north.
  • Orienting Arrow: Use the orienting arrow to position the bezel. The outline of the arrow is shaped to fit the magnetized end of the needle.
  • Orienting Lines: These parallel lines rotate as the bezel moves, aligning with the north-south lines on a map so you can align the orienting arrow north.

Adjust for Declination

Finding north on a map is generally simple thanks to the compass rose that should be printed on it. Magnetic north, where the compass needle points, and true north will be off by a few degrees. This difference is called declination. Declination may vary from nearly 20 degrees east in the state of Washington to nearly 20 degrees west in the state of Maine. It's important to adjust for declination carefully because being off by even one degree can lead to a deviation off course. Find the declination value for your location: Many topography maps will list this, but this value may also change over time. To ensure accuracy, check a map's revision date. Every compass has a specific way to adjust for declination; some require a tool, while others do not. Follow the manufacturer's instructions for your compass to set the declination.

Orient the Map

Reading a map and correlating it to your surroundings is a crucial skill. The first step to successful map-reading involves orienting the map.

  1. Set the compass on the map with the direction of travel arrow pointing at the top of the map.
  2. Rotate the compass bezel to align north with the direction of travel arrow.
  3. Slide the baseplate of the compass until a straight edge aligns with the left or right edge of the map and the travel arrow points toward the top of the map.
  4. Keep the map and compass steady while rotating your body until the magnetic needle of the compass is inside the outline of the orienting arrow.

This completes orientation of the map. Now, you can identify landmarks on the map and coordinate them with what you see around you. Becoming familiar with the map and your surroundings before you move makes it easier to navigate. As you start to move, keep your map handy and look at it frequently to stay on course.

Take a Bearing

When you take a bearing, you are describing a direction, which you may use to proceed on course. Bearings are relative to a specific location: If you use the same bearing in a different position, you would not reach the same destination. It's possible to use a bearing to get to a place if you know your location on a map.

  1. Set the compass on the map to align the straight side of the baseplate between the current position and your desired destination.
  2. Ensure that the direction of travel arrow points toward the destination.
  3. Rotate the bezel to align the orienting lines on the compass with the north-sound grid lines of the map.
  4. Check the index line to take the bearing you've just determined.
  5. Hold the compass with the direction of travel arrow so it points away from you.
  6. Move your body until the magnetized needle aligns with the orienting arrow. This makes the direction of travel arrow face the bearing, and you can now follow it to reach your destination.

Taking a Bearing in the Field

When in the field on a trail, you can use a bearing to determine your location on a map.

  1. Find a landmark around you that you can identify on the map.
  2. Hold the compass flat with the direction of travel arrow so it points away from you and at the landmark.
  3. Move the bezel so the magnetized needle sits inside the orienting arrow.
  4. Check the index line to see the bearing you've captured.
  5. Place the compass on the map and align a corner of the straight edge on the compass with the landmark.
  6. Keep the direction of travel arrow pointed at the landmark. Rotate the baseplate so that the orienting lines run north-south and the north point on the bezel points to north on the map.
  7. Draw a line on the map that matches the straight edge of the compass. The point where the line crosses your trail is your current location.

Use Multiple Bearings to Determine Location

If you are not on a trail, find your location on a map using a process called triangulation. Follow the same steps to take your bearing using two other landmarks. Ideally, these landmarks will be a minimum of 60 degrees away from the first landmark and from each other. After drawing the lines, they should either meet or form a small triangle. If they meet at a single point, that's your location. If they form a triangle, your location is somewhere inside the triangle. If triangulation forms a large triangle, you may have made an error: Redo your work to try to get a small triangle.

Additional Navigational Resources

Reference: https://pixabay.com/en/map-navigation-hands-travel-route-455769/