Open an OS map of the Lake District, Snowdonia or the Highlands and half the place names are words you’d never use at home. A tarn is a small mountain lake. A tor is a rocky outcrop on a hilltop. A corrie is a steep-sided bowl scooped out of a mountainside. A col is the low point on a ridge between two tops. Fell, crag, beck, gill and pike are a northern English hill, a cliff, a stream, a steep stream ravine and a pointed summit.
Knowing what the words mean is handy. Knowing what each one looks like in contour lines is the useful bit, because the name tells you what the ground is going to do before you get there. That’s what this page adds that a dictionary can’t. For every word, you’ll get the meaning, where in Britain you’ll meet it, and the clue that gives it away on the map.
If contours are still a bit of a puzzle, have a quick go on our free contour lines tool first. Every map clue below will make more sense.
What do the words on an OS map mean?
Here’s the quick version. The sections below go through each one properly.
| Word | What it is | Where you’ll meet it | Map clue |
|---|---|---|---|
| Tarn | Small mountain lake | Lake District, northern England | Blue water, often at the bottom of a corrie |
| Tor | Rocky outcrop on a hilltop | Dartmoor, Peak District | Rock symbols on a summit |
| Corrie / cwm | Steep-sided bowl in a mountainside | Scotland (corrie, coire), Wales (cwm), Lakes (cove) | Horseshoe of contours, tight at the back |
| Clough | Steep, narrow valley | Peak District, Pennines | Tight V of contours with a stream |
| Fell | Hill or mountain, or open hillside | Lake District, Pennines | Mostly in names |
| Crag | Steep rock face | Everywhere, especially the north | Cliff symbols, contours bunched or merging |
| Beck | Stream | Northern England | Blue line in a V of contours |
| Gill / ghyll | Steep, narrow stream ravine | Lake District, Yorkshire Dales | Very tight V of contours |
| Pike | Pointed summit | Northern England | Small, tight ring of contours |
| Knoll | Small rounded hill | Everywhere | Small closed contour ring |
| Col / bealach / saddle | Low point on a ridge between two tops | Everywhere; bealach in Scotland | Hourglass shape in the contours |
| Nick | Notch or gap in a ridge or edge | Northern England | A pinch in the contours along an edge |
Water words: what is a tarn, a beck and a gill?
What is a tarn?
A tarn is a small lake in the mountains. The word is used most in the Lake District and the rest of northern England, where you’ll see it all over the map: Red Tarn below Helvellyn, Stickle Tarn above Great Langdale.
Map clue: a patch of blue, often sitting at the bottom of a horseshoe of contours. That’s because many tarns fill the floor of a corrie, so where you see a tarn high up, look for steep ground round three sides of it.
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What is a beck?
A beck is a stream. It’s the everyday word for one across northern England, so you’ll find it in names like Aira Beck, which runs down to Ullswater.
Map clue: a thin blue line. Look at the contours it crosses. They make a V shape, and the V points uphill, upstream. Where the V points downhill instead, you’re looking at a spur, a ridge running down the hillside. That’s the quickest way to tell valley from ridge when you’re working out which way the ground falls. If you go on a navigation course, you’ll hear a small valley like this called a re-entrant.
What is a gill?
A gill, also spelled ghyll, is a steep, narrow ravine with a stream running down it. It’s a Lake District and Yorkshire Dales word. Dungeon Ghyll in Great Langdale is one of the best known.
Map clue: like a beck, but the contours are much tighter and the V much sharper. A gill is steep-sided ground. Its stream can rise fast in heavy rain, and the rock gets slippery, so in wet weather it’s somewhere to be careful rather than a handy shortcut.
Valley words: what is a corrie, a cwm and a clough?
What is a corrie?
A corrie is a deep, steep-sided bowl in the side of a mountain, carved out by ice. The back wall is often a cliff, and the floor is often flat, sometimes with a lake in it. In Scotland you’ll see it spelled coire on the map, as in Coire an t-Sneachda in the Cairngorms, and in the Lake District some are called a cove, as in Keppel Cove below Helvellyn.
Map clue: a horseshoe of contours. Tight and bunched round the back and sides where the walls are steep, opening out towards the mouth. If the bowl has a lake, it’ll be a tarn in England or a lochan in Scotland.
What is a cwm?
A cwm (said “coom”) is the Welsh word for the same thing, a corrie. Cwm Idwal in Snowdonia is the classic example.
Map clue: the same horseshoe of contours as a corrie.
What is a clough?
A clough is a steep-sided, narrow valley, usually with a stream. It’s a Peak District and Pennine word. Grindsbrook Clough, straight up from Edale onto Kinder Scout, is one of the best known.
Map clue: a tight V of contours with a stream in the bottom. On Kinder, the cloughs are some of the most reliable features you’ve got, which is why we use them as handrails in walking from Edale station.
Summit words: what is a tor, a pike, a knoll and a fell?
What is a tor?
A tor is a rocky outcrop standing up on top of a hill. Dartmoor is full of them, granite tors like Haytor, and you’ll find them in the Peak District too.
Map clue: the rock symbols drawn on or near a summit, with the contours ringing the top.
What is a pike?
A pike is a pointed or peaked summit. It’s a northern English word, as in Scafell Pike, the highest mountain in England, and Pike o’ Stickle in Langdale.
Map clue: a small, tight set of contour rings at the top, close together. The closer the rings, the steeper and pointier the top.
What is a knoll?
A knoll is a small, rounded hill or hummock. It’s used everywhere, and it matters more than it sounds, because a knoll can be a useful thing to aim for, or a confusing one on rough ground.
Map clue: a small closed contour ring on its own. Very small knolls may not show at all if they’re lower than the gap between contours.
What is a fell?
A fell is a hill or mountain in northern England, especially the Lake District and the Pennines, and it’s also used for open, unfenced upland. It’s why hill walking there is called fell walking, and why you see it in names like Scafell and Bowfell.
Map clue: mostly in the names rather than a particular shape. Treat “fell” as a sign you’re on proper open hill ground.
Rock words: what is a crag?
What is a crag?
A crag is a steep, rugged rock face or cliff. The word is used all over Britain and especially in the north, as in Dow Crag above Coniston.
Map clue: the cliff and rock symbols, often drawn over contours that bunch together or seem to merge. That’s ground to plan round, not through, particularly in poor visibility.
Gap words: what is a col, a bealach, a saddle and a nick?
What is a col?
A col is the lowest point on a ridge between two summits. A saddle is the same idea, named for its shape. In Scotland you’ll see bealach on the map, as in Bealach na Bà, and for the bigger passes lairig, as in the Lairig Ghru. In Wales it’s bwlch.
Map clue: an hourglass shape in the contours. Two sets of rings for the two tops, with the contours pinching in between them. Cols matter for navigation because they’re natural crossing points and natural places to come down off a ridge. They also funnel the wind, so expect a col to be the windiest spot on the ridge, not the most sheltered.
What is a nick?
A nick is a notch or narrow gap in a ridge or edge. It’s a northern English word, as in the Nick of Pendle in Lancashire.
Map clue: a pinch in the contours along an edge, a small col in miniature.
Why the words matter when you navigate
Place names are clues, not just labels. A tarn high on a mountainside tells you there’s probably a corrie with steep walls round it. A gill tells you the stream on your route runs through a steep ravine. A col tells you where a ridge is easiest to cross.
Read the names alongside the contours and you’ll start to see the shape of the day before you leave the car park or the station.
And the regional words follow the landscape. Fells, becks, gills and tarns in Cumbria; cloughs in the Peak; corries and bealachs in the Highlands; cwms and bwlchs in Wales. Once you know a handful, a new map stops looking like a foreign language.
Want to test yourself? The contour lines quiz asks you to match the ground to the map, which is exactly the skill these words are pointing at.
Frequently Asked Questions
What is the difference between a fell and a mountain?
In northern England, “fell” is simply the local word for a hill or mountain, so the two overlap. The Lake District’s highest summits are all called fells, and fell walking is the local name for hill walking. The word is also used for open, unfenced upland, rather than for a particular height.
What is a corrie in geography?
A corrie is a deep, steep-sided bowl carved into a mountainside by ice, with a steep back wall and often a lake on its floor. The same feature is called a coire in Scotland and a cwm in Wales. On an OS map it shows as a horseshoe of contours, tightly bunched round the back and opening out downhill.
What is the difference between a beck and a gill?
A beck is a stream, the usual word for one across northern England. A gill, or ghyll, is a steep, narrow ravine with a stream in it. On the map, both show as a blue line in a V of contours pointing upstream, but a gill’s contours are much tighter.
What does a col look like on a map?
A col shows as an hourglass shape in the contour lines: two sets of rings for the two summits, with the contours pinching in between them at the low point. Cols are natural crossing points and often the best place to come off a ridge.
What is a tor?
A tor is a rocky outcrop standing up on top of a hill, most famously on Dartmoor, where the granite tors are landmarks across the moor. On an OS map it shows as rock symbols on or near a summit.
Now see them in the contours
Words are the easy half. The skill is seeing a corrie, a col or a gill in the contour lines before you’re standing in it. Our free contour lines tool lets you build the shapes yourself, and when you want the whole of map reading taught in order, from symbols and contours to the compass, that’s what our Mountain Navigation Course does.
Next time you open a map, find one word from this page and work out what the ground will look like before you check. Ask any questions in the comments below.
