Where The Lines Cross Is You
Okay. Last lesson we shot bearings to two peaks. Now we're going to draw those two lines on the map for real and see where they cross. That crossing point is where you're standing. That's triangulation. That's the whole trick.
I know "triangulation" sounds like something a surveyor does with a tripod and a bad attitude. It's not that fancy. It's two lines and an X.
What you're actually doing
You've got two landmarks you can see and identify on the map. A peak, a water tower, a distinct saddle, whatever. You've taken a bearing to each one with your compass, adjusted for declination like we practiced, said the number out loud like we practiced. Now you're going to turn those two bearings into two lines on paper, and wherever those lines cross is you.
That's it. That's the magic. There's no third landmark required, though a third one makes it more accurate, and I'll get to that.
The steps
1. Orient your map to the ground. You know this one by now. Don't skip it just because you're excited to draw lines.
2. Lay your compass baseplate on the map with one corner touching the symbol for your first landmark. The edge of the baseplate is going to be your line. Pivot the whole compass around that landmark symbol until the orienting lines inside the housing match up with north on the map, using the dial setting from the bearing you already took.
3. Draw a line along the baseplate edge, straight through the landmark symbol, going back toward you. Use a pencil. You will mess this up at least once and you don't want it in pen.
4. Do the exact same thing with your second landmark and its bearing. Line, pencil, through the symbol, back toward you.
5. Look at where the two pencil lines cross. That's you. Right there. Little X on the paper is your actual location on the actual ground.
If you've got a third landmark and a third bearing, draw that line too. In a perfect world all three lines cross at one exact point. In the real world you'll usually get a small triangle instead, three lines that almost meet but not quite. That little triangle is normal. Compasses aren't perfect, your reading isn't perfect, your hand isn't perfect. If the triangle's small, you're fine. If it's the size of a dinner plate, something's off and you should recheck your bearings before you trust it.
A caution here
Don't do this while you're moving. I've told you before, I can't take a bearing while walking and I don't pretend to. This is triple true for triangulation, because now you're taking two readings and they both need to be from the same spot. Plant your feet. Take bearing one. Take bearing two. Don't wander between them.
Also, this only works if you know which landmarks you're looking at. If you're guessing which peak is which on the map, you're not triangulating, you're just drawing confident lines to nowhere. Take the extra thirty seconds to actually confirm what you're looking at before you shoot the bearing.
My opinion on this one
I still think the cheap baseplate compass is the right tool here, not the sighting mirror version. Triangulation asks you to lay the compass flat on paper and pivot it around a point, over and over, twice per fix. The baseplate does that cleanly. The mirror compass has more parts to fumble while you're trying to hold a pencil at the same time. Fussier tool, same result. I went back to the cheap one years ago and never looked back.
Why this matters more than it sounds like
This is the skill that turns "I know roughly where I am" into "I know exactly where I am, on this map, right now." That's a different kind of confident. The two-peaks bearing exercise last lesson was practice. This is the actual use of it. Once this clicks, you don't need the trail to tell you where you are. You can figure it out yourself from stuff you can see.
Honestly, this is the one that got me a little smug once. Sat on a rock after nailing a fix off two peaks and a radio tower, dead in the clearing I was standing in. Nobody around to see it. Which, I've decided, is the correct way to feel smug about something. Quietly, to yourself, on a rock.
My sibling Amber and I have had a list of hikes we've been meaning to do together for years now. We've knocked out maybe half of it. Every time I teach this lesson I think about how I should just text her and go do the next one before life gets busy again, which it always does. Anyway. Point is, once you can triangulate, you stop needing an excuse to go find out where you are. You can just go.
Before next time
Grab a topo map of somewhere you actually hike and pick two landmarks you'd recognize from a distance. Next class we'll practice this fix outside, so think ahead about where that might be. Parking lot's fine. It's always fine to start in the parking lot.
Thanks, Jason