Why Contours Matter More Than You Think

Most of us learn the basics of map reading on a lowland footpath, where the biggest navigational challenge is remembering which gate to go through. Then we head for the hills with the same approach, and suddenly the map is covered in squiggly orange lines that we half-ignore in favour of the path. That is a mistake. Contour lines are not decoration; they are the terrain itself, drawn in two dimensions. Learn to read them fluently and you can predict how hard a day will be, where the ground will be boggy, where a crag might drop away unexpectedly, and whether that shortcut across the hillside is a sensible idea or a slow, miserable slog.

The good news is that contour reading is a skill you can build on any walk, from the Cheviots to the Cairngorms. It costs nothing and it makes you safer.

The Numbers Behind the Squiggles

On a British Ordnance Survey map, contour lines usually appear every ten metres of height on 1:25,000 Explorer maps, and every ten or twenty metres on 1:50,000 Landranger maps. The exact vertical interval is printed in the legend, so check it before you trust your instincts. Every fifth line is usually thicker and labelled with its height, which is your anchor for everything else.

Two rules cover most situations:

• Close together means steep. Contours packed tightly show a rapid change in height, so expect a punishing climb or a sharp descent.
• Far apart means gentle. Widely spaced contours indicate flatter or more rolling ground, though "gentle" on a peat plateau can still mean wet, tussocky going.

Where contours converge into a tight V or U shape, look at what is at the point of the V. If the V points uphill and a blue line runs through it, you are looking at a stream in a valley. If it points downhill and there is no water, that is a spur or ridge, often the easiest line of ascent.

Spotting Crags and Steep Ground

Crags are one of the great hidden hazards for anyone who plans routes on paper. A cliff face is effectively a vertical drop, so the map shows contours merging into a single dark line, sometimes with a hachured or rocky edge symbol alongside. In Scotland this can be a genuine problem: a route that looks like a straightforward descent on a 1:50,000 map can turn into a serious scramble over wet rock.

If you see a very tight cluster of contours at the top of a slope, treat it as ground that needs care. Ask yourself:

• Is there a gentler line just to the side, following a spur or a break in the slope?
• Does a path or fence line cross the steep ground, and does that suggest a safe way through?
• Would I be happy descending this in clag, wind and rain, or only on a dry summer afternoon?

Checking the map before you leave, rather than peering over the edge, is what separates a relaxed day from a bad one.

Judging Effort and Pacing

Contours let you estimate how much climbing a route involves, and that matters more than distance for most walkers. A ten-kilometre day with 900 metres of ascent in the Lake District will feel far harder than a twenty-kilometre day with 300 metres in the Chilterns. Add up the height gained section by section and compare it to what you have comfortably managed before.

Use a simple rule of thumb: roughly one minute extra for every ten metres of ascent for a reasonably fit walker with a light pack. Two hundred metres of climb, then, is about twenty minutes of extra effort on top of your flat-ground pace. Steep ground and rough terrain push this up further, so build in margin rather than planning to the minute.

Contour spacing also hints at what is underfoot. Closely packed contours with a broken, complex pattern often mean rocky, broken ground; long smooth slopes with evenly spaced lines suggest grass or heather. Both can be slow going in the wet, but in different ways.

Reading Valleys, Bogs and Water Crossings

Valley bottoms are usually where the contours form wide, flat-floored V shapes, and where streams gather. These are often the wettest places on the hill, with peat hags and boggy ground. If you can see that a valley floor is broad and flat, with contours spaced widely before a sharp rise, expect slow, energy-sapping terrain. Sometimes a higher line along the shoulder of the valley is drier and quicker, even if it adds a little distance and climb.

Streams and rivers, shown in blue, follow the lowest ground, and contour shape tells you how steeply they fall. Where they cross your route, check whether the surrounding contours suggest a narrow, incised gully or a wider, gentler crossing. In spate conditions, small streams on steep ground can become genuinely dangerous, so a route with several crossings is worth reconsidering if heavy rain is forecast.

Putting It Together Before You Go

A good hill route plan is built in layers. Start with your goal, then trace the line on the map and ask of each section: how steep, how rough, how exposed, and how does that match the forecast and the group's fitness and experience?

• Sketch the ascent and descent profiles roughly on paper; the shape often reveals surprises.
• Mark any steep ground, crags or tricky crossings as things to watch for.
• Identify escape routes down easier spurs or into valleys if the weather turns.
• Compare your plan with the day's conditions, not just the summer ideal.

Contour reading is not about memorising symbols; it is about building a mental picture of hills you have never walked. Do it often enough and the map stops being a flat piece of paper and starts feeling like the ground itself. That is when hill days become calmer, better paced and considerably safer.