Reading Contour Lines to Judge Steep Ground

Why contour lines are the best route-planning tool you own

Most of us plan a day out by distance and forget the shape of the ground underneath it. A four-kilometre walk in the Yorkshire Dales can be a cheerful amble or a punishing thrash, and the difference is almost always gradient. Contour lines are the cheapest forecast you will ever get: every line marks a fixed slice of height — commonly 10 metres on British hill maps — and the distance between those lines tells you how much ground you must walk to earn that height.

Learn to read them fluently and you will start choosing routes that match your legs, your time and the weather, rather than discovering the problem halfway up a hillside.

The one rule worth memorising

Closely spaced contours mean steep ground. Widely spaced contours mean gentle ground. Everything else is refinement.

• Lines almost touching: expect something around 1-in-2 or steeper. Crags, scree, clinging heather and hands-on-rock territory.
• Evenly spaced lines a pencil-tip apart: a steady pull, roughly 1-in-5 to 1-in-8. Hard work but honest walking.
• Big gaps, sparse lines: rolling tops, valley floors and plateaux. Here the challenge is navigation and bog, not climbing.
• Bunched at one end, spread at the other: a break of slope. Gentle at first, then abruptly sharp — very common on the limestone scars above Malham and the gritstone edges further east.

One caveat before you trust your eyes: a map draped over a knee bends perspective. When a slope really matters, measure it.

Measuring a slope properly

You can turn a vague impression into a number in under a minute.

• Draw a straight line across the slope, from where you are to where you intend to be.
• Count the contour lines your line crosses and multiply by the contour interval. Twenty lines at 10 metres is 200 metres of ascent.
• Measure the horizontal distance with the scale bar at the bottom of the map, then divide the ascent by that distance.
• Read the result as a gradient. 100 metres of climb over 400 metres of ground is 1 in 4. The same climb spread over 800 metres is 1 in 8 — half as steep and far kinder with a pack.

As a rough working guide, 1 in 4 or steeper will slow a laden group considerably, 1 in 3 will have you stopping every few minutes, and anything near 1 in 2 is a scramble rather than a walk. Naismith's rule will not save you here, because it assumes ground you can walk at a steady pace. Add generous time for steep sections and plan your day around the slowest part, not the average.

Reading the shape, not just the spacing

Spacing tells you how steep; shape tells you what sort of ground it is. Ridges and valleys both bend the contour lines, and the direction of the bend is a free gift of information.

• A V pointing downhill marks a spur or ridge. These are usually the driest, firmest and most efficient lines of ascent — nature's staircase.
• A V pointing uphill marks a gully, re-entrant or stream valley. Expect wet ground, loose material, bracken and the occasional awkward step.
• Long, unbroken straight contours suggest a uniform slope. Whether that is springy turf or loose scree depends on the rock beneath.
• A tight band with gentle shelves above and below is the classic scar or edge profile. You can usually find a way around the band rather than through it.

Add aspect to your thinking. In the Dales, north-facing slopes hold damp, shade and late-lying snow, while south-facing ground dries quickly and is often friendlier underfoot in winter and early spring.

Putting it to work in the Dales and beyond

Take Ingleborough from the Ribblehead side: the contours on its northern flanks crowd into long, unrelenting bands, while the approach from Ingleton eases and steepens in steps that are far easier to pace. Whernside and Great Whernside show similar patterns, with steep flanks softened by long shoulders. In Wharfedale and Swaledale the same story plays out in miniature: short, sharp climbs straight up from the road, then broader, lazier ridges where the lines spread apart and the walking relaxes.

The habit transfers to the wider British countryside. Lakeland passes, Snowdonia's flanks, the rounded shoulders of the Cheviots and the great Cairngorm plateaux all declare their character in contour spacing long before you arrive.

Making the call on the day

Before you leave the car park, run the route through a few questions.

• Where are the tightest bunches of contours, and can I avoid them?
• Is my ascent following a spur, or fighting up a gully?
• Have I timed the steep sections honestly, not just the distance?
• What is my escape route if the ground turns out wetter or looser than the map suggests?

A map is a promise about height, not about ease. The contours give you the height for nothing; the judgement is yours. Practise on short local walks — pick a slope you know well, count the lines, calculate the gradient and then compare it with what your legs remember. Do that a dozen times and you will read a hillside at a glance, long before you ever set foot on it.