Why “triangulation” to get unlost may be a bad idea


Many navigation books, videos and classes teach a slick-sounding technique known as “triangulation" (or “resection”) to locate your position on a map if you’re lost.

In theory, it works like this:

From your position, you take a compass bearing on two or more visible landmarks, which you can recognize and locate on your map. If you then plot these bearings correctly onto your map, the intersection of the lines is your approximate position.

This sounds great practicing on your cozy kitchen table. But, for triangulation to work, you need three variables to ALL line up in your favor.

Here are those three, and some reasons why this technique often fails in practice.

  1. Triangulation requires that you can actually see two or more features on which to take a bearing. If you’re lost in heavy tree cover, at night or in low visibility, you’re out of luck.

  2. Triangulation requires that can match the feature you see in the field to your map.You’re lost, but it’s daylight and you’re able to see several nearby peaks. Trouble is, you are not sure of their names. Being able to see and take a bearing to a peak, lake or other feature is useless unless you can positively identify the feature on your map.

  3. Triangulation requires that the feature you see in the field actually be ON your map. You’re lost on Mt. Hood, but you can see Mt. Jefferson, 50 miles away. Too bad, Mt. Jefferson is not on your map, making that feature useless for triangulation.

You can see that the triangulation technique has a host of flaws. There are rare times when it works, but don’t rely on it alone to get you unlost.

So, what can you do? Always have a quality GPS app on your phone, such as Gaia GPS, they can show you your current position overlaid on a base map. Or, at the very least, have an app that can tell you your current position in UTM coordinates, which you can then plot onto the paper map you’re carrying, which hopefully has a UTM grid printed on it.

To close on a slight positive note, sometimes just getting a single bearing to a feature and maybe plotting it on your map can be a big help. At least you know you are somewhere on that plotted line.

I heard a story from a Search and Rescue (SAR) guy about a lost hunter who called 911. They put him in touch with the local SAR team. The rescue team asked him if he had a compass, and if he could take a bearing to any landscape feature around him he recognized. “Sure thing”, the hunter says, “from where I’m standing, I can take a bearing of 240° to Peak XYZ”

“Great” says the SAR team, “stay right there and we’ll come get you.” It may not sound like much to know that you are on a specific line from a specific terrain feature, but by definition, that excludes every other line that you could be on. All the rescue team had to do was walk on that same bearing toward the peak, until they found the hunter.

The story came from a decade or so back when people did not have good navigation apps on their phone. These days, everybody who goes into the backcountry should have a way to find coordinates from their phone and know how to transmit them to emergency services.