So, you’ve got an OS map in front of you and it looks completely overwhelming. Brown squiggles everywhere. Coloured shapes. Tiny symbols. Numbers that seem to mean absolutely nothing.
You are not alone. Every single person I’ve taught from scratch has stood there with that same expression.
The short version: an OS map is five things, and you can learn them one at a time. The scale tells you distance, the legend tells you what the symbols mean, the blue grid tells you exactly where you are, the brown contour lines tell you the shape of the ground, and orienting the map lines all of it up with what is in front of you. Get those five and the rest is practice.
But here’s the thing: the map is not complicated. It just needs explaining properly. This is map reading for beginners, and by the end of this guide you’ll understand how to pick the right map, read the symbols, pinpoint your location with a grid reference, understand what the land looks like from the contour lines, and point yourself in the right direction.
Reading the map is one piece of a wider skill set. If you want to see where it fits alongside compass work and route planning, our complete guide to navigating on foot covers the whole picture.
A quick note on what OS means. Ordnance Survey is the UK’s national mapping agency. They’ve been mapping Great Britain for over 200 years, and their maps are the standard for anyone heading into the hills. When someone says “OS map,” this is what they mean.
Let’s take it one step at a time.
How to Choose the Right OS Map Scale
Before you can read a map, you need the right one. And understanding how to read a map scale is where it starts.
Scale tells you how much the real world has been shrunk down to fit on the page.
OS Explorer (1:25,000 scale) is the one you want for walking. Every 4 centimetres on the map equals 1 kilometre on the ground. It shows field boundaries, individual footpaths, and even the local pub.
OS Landranger (1:50,000 scale) covers a larger area with less detail. Fine for cycling or planning long-distance routes, but for walking in the hills it’s not detailed enough.
For foot travel, always use the Explorer. The extra detail matters, especially once the footpath splits three ways and you’re trying to work out which one is which.
How to Read OS Map Symbols (The Legend)
Open any OS map and you’ll see a legend along the edges. That’s the key to everything on the page.
Every symbol is explained there. It’s the first thing to look at before you start navigating.
You don’t need to memorise every symbol. A few are worth knowing straight away.
Blue lines and areas are water features, such as rivers, lakes, marshes.
Green areas are woodland and forest.
Green dashed lines are crucial. These mark public rights of way, the footpaths and bridleways you’re legally allowed to walk.
Black dashes typically indicate tracks or field boundaries.
Over time, symbols like a church with a tower or a rocky outcrop start jumping out automatically. For now, just keep the legend handy and check it whenever you’re unsure. There’s no shame in that, and even experienced navigators do it.
The full OS map symbols guide is available to download free from the Ordnance Survey website.
How to Use Grid References to Pinpoint Your Location
This is where a lot of beginners start to panic. Don’t.
A grid reference is simply a way of describing exactly where something is on the map, using a pair of numbers. It’s also the information Mountain Rescue will ask for if you ever need to call them, so it’s genuinely worth knowing how to read a grid reference on an OS map.
Look at your OS map and you’ll see a faint grid of blue lines. These are the National Grid lines. They divide the whole of Great Britain into a network of squares.
The vertical lines are called Eastings. Their numbers increase as you move east.
The horizontal lines are called Northings. Their numbers increase as you move north.
To read a grid reference, use this rule: along the corridor, then up the stairs. Read the Easting number along the bottom first, then the Northing number up the side.
A 4-figure grid reference gives you a 1 kilometre square. That’s a useful starting point, enough to find a car park or a summit.
For more precision, use a 6-figure grid reference. You divide each square into ten equal parts and read to the nearest tenth. That narrows your location down to within roughly 100 metres. Accurate enough to give a precise location to Mountain Rescue if you need it.
We cover how to use grid references in detail inside the Mountain Navigation Course.
| Reference | Pins you to | When you would use it |
|---|---|---|
| 4 figures (3377) | A 1 km square | Rough planning, naming a broad area |
| 6 figures (336 774) | A 100 m square | The everyday one. What you give Mountain Rescue |
| 8 figures (3363 7742) | A 10 m square | Pinpointing a small feature, mostly from a GPS |
The only way this sticks is doing it, so have a go on our free grid reference practice tool. It gives you a point and checks your answer.
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How to Read Contour Lines
Right, this is the big one. Contour lines are what turn a flat sheet of paper into a 3D picture of the landscape. Once this clicks, the whole map makes sense.
A contour line joins all the points on the map that are at the same height above sea level. On a 1:25,000 Explorer map, each line represents 5 or 10 metres of height change.
The spacing tells you how steep the ground is. Lines packed tightly together mean a steep slope, a hard climb or a sharp drop. Lines spaced well apart mean gentle, flat terrain.
The shape tells you what kind of feature you’re looking at. Concentric circles closing in on a point indicate a hill or summit. A V-shape pointing uphill (into higher numbers) indicates a valley. The same V-shape pointing downhill is a spur, a ridge pushing out from the hillside.
It might look complicated at first. Practise by picking any point on the map and tracing the contours outward from it. You’ll start to see the shape of the land in your mind before you’ve left the house.
We’ve got a full guide on how to read contour lines on an OS map if you want to go deeper on this.
Contours are the skill that takes longest to click. How to read contour lines on an OS map goes through each shape slowly, and the free contour lines quiz will show you whether it has landed.
How to Orient Your Map
A map is useless if it’s pointing in the wrong direction. Orienting your map means aligning it so that what’s in front of you on the ground is also in front of you on the map.
The simplest way to do it is visually. Find a clear feature in front of you, a road, a river bend, a hill, and rotate the map until that feature lines up with what you can see in real life.
If you have a compass, it’s even easier. Place the compass on the map and rotate yourself (with the map) until the red needle points north on the map. Everything should then match up with your surroundings.
This one habit makes a significant difference. I’ve seen walkers confidently heading the wrong direction because their map was facing south. Once you make map orientation a default habit, that stops happening.
To go further with the compass side of things, take a look at our guide to how to take a compass bearing on an OS map.
Putting It All Together
Map reading for beginners doesn’t need to be complicated. Here’s the recap.
- Scale, use the 1:25,000 Explorer for walking
- Symbols, keep the legend handy, check it freely
- Grid references, along the corridor, up the stairs
- Contour lines, spacing means steepness, shape means feature type
- Orient the map, always, every time you stop
The best way to build confidence is to take a map somewhere you already know well and practise reading it in both directions. Look at the ground, find it on the map. Look at the map, find it on the ground. Twenty minutes of that will teach you more than any amount of reading about it.
If you want structured map reading training that covers all of this plus bearings, route planning, and emergency navigation, Bondringo’s Mountain Navigation Course walks you through every skill at your own pace, from home, before you head out.
Orienting the map is the first thing a compass is for, and how to use a compass on a map covers the rest, including taking and walking a bearing.
What is the difference between a 1:25,000 and a 1:50,000 OS map?
The numbers refer to scale. On a 1:25,000 OS Explorer map, 4 centimetres represents 1 kilometre on the ground. On a 1:50,000 OS Landranger, 2 centimetres represents 1 kilometre, so you’re covering more ground on the page but with less detail. For walking and hiking, the 1:25,000 Explorer is the right choice. It shows individual footpaths, field boundaries, and terrain features the Landranger leaves out.
How do I read a grid reference on an OS map?
Use the rule “along the corridor, up the stairs.” First read the Easting number along the bottom of your target square, then the Northing number up the side. A 4-figure grid reference gives a 1km square; a 6-figure reference (where you read each to the nearest tenth) narrows it to within about 100 metres. That’s the level of precision Mountain Rescue will ask for if you need to call them.
What do contour lines tell you on an OS map?
Each contour line connects points of equal height above sea level. On a 1:25,000 Explorer, lines are 5 or 10 metres apart. Tightly spaced lines mean steep ground; widely spaced lines mean gentle terrain. V-shapes pointing uphill (into higher contour numbers) indicate valleys; V-shapes pointing downhill indicate spurs. Once you get your eye in, you’ll start reading the 3D shape of the land directly off the map.
Do I need a compass to read an OS map?
Not for basic map reading. You can do a lot by matching features on the map to what you can see around you. But a compass makes orienting the map far more reliable, especially in poor visibility or on featureless terrain. If you’re heading into the hills, carry a compass and learn to use it alongside your map.
Where can I buy an OS map?
OS maps are available from the Ordnance Survey website, and from most outdoor shops, including Cotswold Outdoor, Blacks, and Go Outdoors. You can also access digital OS maps through the OS Maps app, where Explorer and Landranger layers are included with a subscription.
