Triangulation with Compass


Triangulation is the process of pinpointing the location of something by taking bearings to it from two remote points.
Forest fire lookout towers used triangulation to locate spot fires.
A ranger at Tower A would see smoke in the distance and take a bearing to it on his compass. This single line was not enough information to locate the fire because it could be anywhere along that line, close or many miles away.

The ranger would radio Tower B and tell him the general direction of the fire. Tower B would then find the fire from his viewpoint and take a bearing. Where the two bearings crossed would pinpoint the fire and firefighters could be efficiently dispatched to put it out.

Sometimes, a third tower would be used to verify the location, but two readings are all that is usually necessary. If a fire occurs directly between two towers or off in a direction that causes their bearings to be similar, then a third bearing is necessary.

This type of triangulation is used by two fixed spots to find a third unknown spot. What you need to do while in the outdoors is similar, but you need to find out where you are, not where something else is.

Finding Yourself

In order to successfully triangulate, known features must exist on your map. In other words, you must have some idea of where you are or be able to identify a well-known landmark from your viewpoint.

By taking bearings to the distant landmarks, you can plot your current location on your map in this way:

If you are standing on a known landmark such as a road, river, or ridgeline but don't know where on that landmark you are, a single remote landmark is enough to plot your position. Where your bearing line to the remote landmark and the landmark you are on intersect is where you are - as long as you take accurate readings and transfer them accurately. :-)

Triangulation Example

triangulation image This example will step you through the process of triangulating your location based on bearings to two or more known landmarks.

Look at this section of map - it has mountains, streams, and hills as indicated by the shaded relief enhancements. Notice it does not have contour lines but that doesn't matter when we are just finding directions.

You might find it useful to print the image and actually do these steps.
Print the map and lay it on the floor.
Orient the map for North right where you are and imagine that you can see mountains off in the distance.

You have just climbed the plateau in the southwest, coming up from the southwest. You do not know at which of the 4 red spots you are currently standing, but you can see 3 mountains off in the distance towards the north and east.

compass triangulationtriangulation using map and compassmap coordinates
For your triangulating, you take bearings to the mountains and get:

To simulate taking each of these bearings, turn your compass dial until that bearing is at the index pointer. Then, turn the compass until RED is in the Shed and the direction-of-travel arrow will be pointing along that bearing.

Transfer your bearings to the map and find out where they intersect. If you oriented your map, took correct bearings, and transferred them accurately, your map should look close to:

map triangulation solution

Now you know where you are on the map and in the real world. If you didn't do too good on this one or want to try another, here's another exercise to try.

Next: Plotting a Route
learn triangulation skills Why was longitude boiling mad?
Because it was 360 degrees

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