Why contours deserve more of your attention

Most of us learn to read a map by following the coloured lines. Footpaths, bridleways, the blue of a stream, the green edge of a forest — these are the things we notice first. Contours sit in the background: thin, brown, faintly tedious, easy to ignore once you have found the path you intend to walk.

That is a shame, because contours are the only thing on the map that tells you how the ground will actually feel under your boots. A path drawn straight up the page might be a gentle amble across a mossy shoulder or a lung-burning wall of wet grass. The colours will not tell you. The contours will.

Reading gradient well is a genuine safety skill as much as a planning one. It is what lets you decide whether a route matches your experience, your knees and the amount of daylight you have left.

The grammar of contour lines

Every contour joins points of equal height. On the standard 1:25,000 walking maps, contours are usually drawn at 10-metre intervals, with every fifth line thicker and labelled with its height. Always check the interval before you set off. On a 5-metre interval map the lines sit twice as close together for the same ground, so the same spacing means something quite different.

Once you know the interval, the basic vocabulary is simple:

• Close together — the ground climbs or drops quickly.
• Widely spaced — gentle ground, a shelf, or a plateau.
• Evenly spaced — a steady, consistent slope you can settle into.
• Bunched, then spaced — a change of gradient, often where a slope steepens into a break or eases onto a shoulder.

Read contours in threes and fours rather than one at a time. The shape of a group tells you more about a hillside than any single line.

Judging gradient: a simple rule of thumb

Many walkers never work out what contour spacing actually means in terms of steepness. It is easier than it looks. On a 1:25,000 map, 1 cm on the paper equals 250 metres on the ground, so 4 mm equals 100 metres.

Now count. If the contours are 4 mm apart and the interval is 10 metres, you climb 10 metres in 100 — a gradient of 1 in 10, around six degrees. That is comfortable uphill walking, the sort you can hold a conversation through. At 2 mm apart you are on 1 in 5, roughly eleven degrees: steady, sweaty work that will slow a group down. At 1 mm apart you are looking at something like 1 in 2.5, and on grass or loose rock that means hands on the ground.

You do not need to measure precisely. Get into the habit of asking whether the lines are "finger-width", "pencil-width" or "touching", and translate that into effort.

Spotting steep ground before you get there

Contours rarely tell the whole story on their own. Combine them with the other symbols on the map.

• Cliff symbols and hachures. Where contours crowd and black crag markings appear, expect rock, not just steep grass. In mist, that is your cue to keep away from the edge.
• Re-entrants and spurs. Where a stream cuts into a slope, the contours bend into a V pointing uphill. That is a re-entrant — often a damp gully, and often the steepest way up. Where the contours bulge out downhill, you have a spur or nose: usually drier, often a nicer line of ascent.
• Convex and concave slopes. A convex slope is gentle at the top and steepens below. From above, the lower ground is hidden, so what looks like a short drop can carry on out of sight. A concave slope is the reverse, and you can usually see the whole thing laid out beneath you.
• The top of the climb. Count the contours to the summit. A dozen closely spaced lines before the cairn means the last stretch will bite.

Turning gradient into time and energy

Gradient is the main reason a walk takes longer than the distance suggests. The old rule of thumb is roughly 5 km per hour on the flat, plus an extra hour for every 600 metres of ascent. That works out at about ten minutes for every 100 metres climbed — ten contours at a 10-metre interval.

Add time on top for bog, tussock, pathless heather and rough boulder fields. Steep ground slows you in both directions: a 1 in 3 grass descent is slower and harder on the knees than a gentle track, and much slower again when it is wet.

The map also shows you where to break a climb. Look for a flattening, a shelf, or a change in the contour pattern where you can stop, eat something and reset. Planning those pauses into the route is far more effective than hoping to find one.

Building the habit

The best way to learn is on a hill you already know well. Before you leave the car park, look at the first climb on the map and guess how steep it will be. Walk it. Compare what you felt with what you saw. Do that often enough and you will start reading gradient as quickly as you read a path.

Contours describe the ground. You still decide whether to walk it, and whether the weather, the wind, the daylight and the energy of the group make it a sensible choice. Used well, they turn a route from a line on paper into a picture of the day you are about to have.