Finding Declination On Your Map
Okay. Last lesson we talked about why the two norths disagree. Magnetic north and true north are not the same spot, and your compass only knows about one of them. Now we have to go find the actual number for where you're standing, because "there are two norths" doesn't help you unless you know how far apart they are here, in Utah County, right now.
Where to find it
Every USGS topo map has this printed on it somewhere, usually down in the bottom margin near the scale bar. Look for a little diagram with three arrows fanning out. One says True North, one says Magnetic North, one might say Grid North. Next to it there's a number, something like "13° E" or "12.5° E."
That number is your declination. It's how far magnetic north is drifting off from true north, from where you're standing.
If you're using a newer map, or one you printed off a website, sometimes that diagram isn't there. In that case you look it up. There are free declination calculators online where you punch in your location and it spits out the number. I'd tell you the site, but honestly, just search "declination calculator" and use whatever comes up. It changes over time anyway, so I don't love printing it in a course and having it go stale on you.
Here in Utah, we're currently sitting around 10 to 11 degrees East, give or take, depending on exactly where in the state you are and what year the map was printed. That's not nothing. Ten degrees off, over a mile, can put you a couple hundred yards from where you meant to end up. That's the wrong side of a hill, easy. Ask me how I know.
Old maps lie to you a little
Declination isn't fixed. It drifts slowly over years. If your dad's old scouting map from twenty years ago says 14 degrees, that number is not necessarily still true today. The magnetic pole wanders. Nobody tells you that either, apparently, same as the metal thing.
So step one, practically: check the print date on your map before you trust the declination number on it. If it's old, look the number up fresh instead. Takes thirty seconds online.
Building the habit, not the memory
This is the part I actually care about teaching. Knowing the number doesn't help you if you forget to use it when you're standing in a parking lot or up a canyon with your hands cold.
So here's what I want you to do every single time, out loud if you have to, even if it feels silly:
- Find the declination number on your map, or look it up if the map's old.
- Say the direction out loud. "East" or "West." This matters, don't skip it.
- Adjust your compass or your math accordingly, before you take a single bearing.
I do this every time, no exceptions, even on trails I've hiked a dozen times. Not because I don't trust my memory in general. I don't trust anyone's memory for this specific thing, including mine. Declination will get you if you treat it like something you know instead of something you check. That's the whole opinion, and I'll die on it same as the ziploc bag thing.
Practicing this at home
You don't need to be outside for this part. Pull out your map at your kitchen table.
- Find the declination diagram or look the number up for your address.
- Write it on a sticky note and put it on the map itself, so you're not hunting for it later.
- Practice saying the adjustment out loud, like you're about to take a bearing. "Declination here is eleven East. Add eleven when going map to field, subtract when going field to map." Say it enough times it stops feeling like a math problem and starts feeling like a reflex.
That's it. That's the whole lesson, mechanically. The hard part isn't the math, it's making yourself do it every time instead of assuming you remember.
One thing I'll mention here even though it's not strictly a declination topic. People ask me if you can adjust for declination while you're walking, on the move, doing the math in your head as you go. I can't do that smoothly and I don't pretend to. I stop, plant my feet, do the adjustment, take my reading, then I walk. It's not the fastest way. It's the honest way, and it's still plenty fast for anything you'll be doing on a trail around here. If someone tells you they can do it all walking without breaking stride, that's fine for them. I'm not that guy, and you don't have to be either.
Before next time: Find your own home address's declination online and write it down somewhere you'll actually see it again, maybe on your phone or taped inside whatever map case you're using.
Thanks, Jason 😎