How to Do a Resection With a Map and Compass

If you can locate two or more distant terrain features on a map, you can use resection to pinpoint your exact location.

Instructions

Difficulty: Moderately challenging

Things You’ll Need:

• Protractors
• Mechanical Pencils
• Scrap Notebook Papers
• Base Plate Compasses
• Straightedges

1. Pinpoint a distant feature of the terrain such as a hilltop, stream or road junction on the map.
2. Using a compass, measure the exact magnetic direction from where you are to the feature.
3. Convert the magnetic direction to a map north direction by subtracting the magnetic variation provided on the map (there should be a small diagram on the map that helps you accomplish this).
4. Calculate the reverse direction of the map north direction (180 degrees from map north).
5. Put the center point of a protractor on the exact map location that you sighted to with your compass.
6. Line up the 0-degree mark on the protractor with map north.
7. Make a mark on the map next to the protractor at the number of degrees of the reverse direction.
8. Remove the protractor and draw a long line with a straightedge and mechanical pencil from the pinpointed distant terrain feature through the mark you just made.
9. Double-check your calculations. You are located somewhere on this line.
10. Pinpoint a second distant feature and repeat steps 1 through 8. You are located where the two lines intersect.
11. Repeat the process with a third distant landmark to confirm your work, if possible.
12. Check your calculations if there is a large difference between the points of intersection.

Tips & Warnings

• Practice resection before you are actually lost.
• If you are on or alongside a linear terrain feature, such as a trail or river, you can pinpoint your location by finding the point at which one line of resection intersects the linear terrain feature.