Triangulation (Resection)
Also called: resection, triangulation, find your position, fix your position, where am I
Sight two or three known landmarks with your compass, convert the bearings, and draw lines on the map. Where they cross is roughly where you are.
- Type
- Techniques
- Needs
- Map, compass, pencil, and two or three landmarks you can name on the map
- Steps
- Sight a landmark, correct for declination, take the back bearing, draw the line from the landmark, repeat
- Best angle
- Landmarks about 60 to 120 degrees apart give a sharper crossing
- Three lines
- Form a small triangle; you are probably inside it
- Used for
- Hiking & camping, Hunting, Fishing & boating
What it is good for
- Finding your position when you can see peaks, towers, or lakes but have no trail.
- Checking a GPS or a guess about where you are.
Where it falls short
- Needs recognizable landmarks, which thick woods may hide.
- Small bearing errors make a big error on the map when the landmarks are far away.
- It takes practice, so learn it on a known spot first.
Tips
- Choose landmarks that are not too close to each other in direction.
- Plot lines lightly in pencil, and keep your declination in mind.
- Take more than two bearings to catch a mistake.
Works well with
- Back Bearing: the bearing you actually plot.
- Lensatic Compass: sights landmarks very precisely.
- Orienting a Map: do it first.
Field notes
If you can see two places you can name on the map, you can place yourself on the line between each and you. The spot where the two lines meet is your position, and a third line checks the work.
Related guides
Numbers here are typical, and values such as magnetic declination change over time and place, so check a current source such as NOAA or your map's legend. Practice near home before you rely on a skill far from help, carry a paper map and compass as a backup, and tell someone your plan. Rules on electronics, land access, and trespass differ by state; our state resources directory links to each state's official regulations. Want a step-by-step guide? Read Trail Navigation Basics.