What happens if your phone dies halfway up a hill?
Here is the short version. Using a compass on a map comes down to three moves. Lay the compass edge along the line you want to walk, turn the bezel until the lines inside it match the grid lines on the map, then turn your body until the red needle sits inside the orienting arrow and walk that way. Everything else is detail on top of those three.
After 15 years as an outdoor instructor, the walker standing in mist staring at a blank screen is the moment I see again and again. A map and compass need no signal and no battery, they work in cloud and rain, and the process is genuinely not complicated once someone breaks it down.
That is what we are going to do here.
Which map do you need?
Before you touch the compass, you need the right map in your hands.
In the UK that means an Ordnance Survey Explorer map at 1:25,000 scale. At that scale, 4 centimetres on the map is 1 kilometre on the ground.
Why does it matter? Because at 1:25,000 you get proper detail. Field boundaries, every contour line, and the green dashed lines that mark public rights of way. That is the level of detail you need to navigate safely on foot.
Do not use a road atlas or a tourist leaflet. They are designed for driving, not for navigating on the hills. On any upland route, detail is the difference between knowing where you are and guessing.
If you want the full explanation of the numbers, we cover it in how to read a map scale, and OS map numbers will find the right sheet for your area.
How does the map’s grid system work?
Right, before you pick up the compass, we need to make sense of those faint blue lines crossing your OS map. They are the National Grid, and they are your best friend once you can read them.
- Eastings are the vertical lines. The numbers increase as you move east.
- Northings are the horizontal lines. The numbers increase as you move north.
Worth practising before you need it. Our free grid reference practice tool drops a point on a map and checks the reference you give back, which is a lot less stressful than working it out for the first time with a casualty next to you.
You always read eastings first, then northings. The classic memory trick is along the corridor, then up the stairs.
A 6-figure grid reference pins your location to a 100-metre square. If you ever need to call Mountain Rescue, that is the first thing they will ask for. Worth knowing before you need it.
What are the parts of a compass?
It might look complicated at first, but a baseplate compass has only five parts you need to know.
- The baseplate is the clear plastic body. You place it flat on the map.
- The direction of travel arrow at the top of the baseplate. It points the way you want to go.
- The rotating bezel, the dial marked 0 to 360 degrees. You turn this to set your bearing.
- The orienting lines and arrow printed inside the base of the housing. These line up with the grid lines on your map.
- The magnetic needle, which spins inside the housing. The red end always points to magnetic north.
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What does setting the map mean?
Setting the map means turning it so the features on the paper match the features in front of you. It is the first thing I teach and the step most beginners skip.
Skip it and you can walk 180 degrees the wrong way. I have seen that happen to experienced walkers who got complacent, not just beginners.
- Hold the map flat in front of you.
- Place the compass flat on the map.
- Turn your whole body, map and compass together, until the red end of the needle points to the top of the map, running with the vertical grid lines.
Now a hill on your left on the map is a hill on your left in real life. Do this every single time you stop to look at the map, until it is automatic.
Why don’t your compass and your map agree?
Because there are three different norths, and your compass only finds one of them.
| What it is | Does it move? | |
|---|---|---|
| Grid north | The direction the blue grid lines run up your OS map | No. It is printed on the paper |
| True north | The actual North Pole | No, and walkers can mostly ignore it |
| Magnetic north | Where the red end of your needle points | Yes, year on year |
The angle you care about is the one between grid north and magnetic north. Ordnance Survey and the British Geological Survey both call it the grid magnetic angle, or GMA. You will also see it called magnetic declination or magnetic variation.
The bit that has changed
Magnetic north has been drifting, and the line where the difference is zero has been sweeping westwards across Britain at roughly 20 kilometres a year.
Ordnance Survey and the British Geological Survey tracked the point where all three norths line up leaving England at Berwick-upon-Tweed in December 2025. It reaches the Scottish coast towards the end of 2026, and after that the whole country is on the other side of the line.
In practice that means two things. The angle is currently very small almost everywhere in the UK, and older advice about adjusting a couple of degrees west is now out of date for much of the country. It also means the figure printed in your map margin was correct when the sheet was printed and is drifting away from correct ever since. Ordnance Survey say as much themselves.
So do not take a number from an article, this one included. Look up the current grid magnetic angle for your area and today’s date using the British Geological Survey grid magnetic angle calculator.
When does it actually matter? On a short leg across ground where you can see features, a degree or two changes nothing you would notice. On a long leg over a featureless plateau in cloud, small errors compound with every hundred metres. That is when you check.
How do you take a bearing, step by step?
This is the skill that lets you navigate in poor visibility, across featureless ground, or when the footpath simply disappears.
- Line it up. Put the edge of the baseplate on the map, joining where you are to where you want to go. Check the direction of travel arrow points at your target, not back the way you came.
- Turn the dial. Rotate the bezel until the orienting lines inside the housing run parallel to the north-south grid lines, with the north marker pointing to the top of the map. The number at the index line is your grid bearing.
- Adjust for the grid magnetic angle, if it is worth it. Apply the current figure for where you are. Over a short leg you can usually leave it.
- Box the needle. Take the compass off the map, hold it flat in front of your chest, and turn your whole body until the red needle sits inside the orienting arrow. You will hear this called red in the shed.
- Walk. Follow the direction of travel arrow.
Turn your body, not the bezel. Once the bearing is set in step 2, the dial does not move again. Fiddling with it on the hill is the most common way people end up walking the wrong line.
Practise this in a park or somewhere familiar before you rely on it in the hills. You want the steps automatic before you are standing in mist at 800 metres.
And if you take that bearing and still cannot work out where you are, here is what to do if you get lost.
Where to go next
Map and compass skills take an afternoon to learn and a lifetime to trust. The more you practise on familiar ground, the more automatic they become when you genuinely need them.
Once you are comfortable with a compass, the next skill to build is reading the shape of the land. Our guide to reading contour lines on an OS map shows you how to picture the ground before you have left the house.
Here is your practice. Take a bearing at home, from your front door to a local landmark, and do it a few times until the steps feel automatic.
Free course: if the honest answer is that your phone is currently your whole navigation plan, the free Digital Safety Net course is built for exactly that.
And if you want a full structured programme covering every navigation skill, from grid references to navigating in poor visibility, the Mountain Navigation Course walks you through it step by step. It is designed for exactly this point in your walking journey, when you want to move past following a GPS and start genuinely reading the ground.
Ask any questions in the comments below.
What is the difference between grid north and magnetic north?
Grid north is the direction the vertical blue lines on your OS map point, and it is what you take a bearing against because it is printed on the paper. Magnetic north is where your compass needle actually points, and it drifts year on year. The angle between the two is called the grid magnetic angle, and it is the figure you apply when you convert a bearing taken off the map into one you walk on the ground.
Do I need to adjust for magnetic declination in the UK?
Check rather than assume. The angle between grid north and magnetic north across the UK is currently very small, and it has been moving from west to east as the line of zero difference sweeps across Britain. Older advice about adjusting a couple of degrees west is out of date for much of the country. Look up the current grid magnetic angle for your area with the British Geological Survey calculator. On a short leg with visible features it makes no practical difference; on a long leg across featureless ground in poor visibility it is worth getting right.
Which way do I adjust, east or west?
It depends where you are and when you are asking, which is exactly why the old mnemonic is now risky. Generations of UK walkers learned “grid to mag, add” because magnetic north sat west of grid north for as long as anyone could remember. Britain is currently in the middle of that switching over, so memorising a direction is the wrong approach. Look up the current figure for your location, note whether it is east or west, and work from that.
Why is the figure on my map margin wrong?
Because it was only ever right on the day the sheet was printed. Ordnance Survey say as much themselves: the grid magnetic angle given on a map is correct at the time of printing. Magnetic north keeps moving, so the older your map, the further that number has drifted. The scale, the grid and the contours on an old map are all still fine. It is only the magnetic figure that goes stale.
Can I use my phone compass instead of a baseplate compass?
You can in a pinch, but not as your main navigation tool on the hills. Phones lose battery quickly in the cold and touchscreens stop responding in rain or with wet gloves. You also cannot lay a phone edge along a map to take a bearing the way you can with a baseplate. A decent baseplate compass costs around £15 to £30 and will outlast a dozen phones. Chuck one in your rucksack and leave it there.
How long does it take to learn map and compass navigation?
The basics, setting a map and taking a bearing, can be understood in an afternoon. Getting confident with them takes a few practice sessions on ground you already know. Most walkers find that after three or four outings where they deliberately navigate by map and compass rather than phone, it starts to feel natural.
