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.
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Things You'll Need
- Protractors
- Mechanical Pencils
- Scrap Notebook Papers
- Base Plate Compasses
- Straightedges
Instructions
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1
Pinpoint a distant feature of the terrain such as a hilltop, stream or road junction on the map.
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2
Using a compass, measure the exact magnetic direction from where you are to the feature.
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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).
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4
Calculate the reverse direction of the map north direction (180 degrees from map north).
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5
Put the center point of a protractor on the exact map location that you sighted to with your compass.
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6
Line up the 0-degree mark on the protractor with map north.
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7
Make a mark on the map next to the protractor at the number of degrees of the reverse direction.
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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.
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9
Double-check your calculations. You are located somewhere on this line.
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10
Pinpoint a second distant feature and repeat steps 1 through 8. You are located where the two lines intersect.
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11
Repeat the process with a third distant landmark to confirm your work, if possible.
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12
Check your calculations if there is a large difference between the points of intersection.
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1
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.
