Using Contours to Judge Hills on a Map

Contour lines are the quiet workhorses of a walking map. They look like ripples on a pond, but each one is a line of equal height above sea level, and the way they bunch, fan and bend tells you almost everything you need to know about the shape of the ground underfoot. Learn to read them properly and you can judge whether a lane is a gentle amble or a lung-burning pull before you have even laced your boots.

What the spacing tells you

On most British walking maps the contour interval is 10 metres, with every fifth line drawn thicker and often numbered. The vertical distance between lines never changes, so the horizontal spacing is where the information lives. Lines close together mean the ground is rising or falling quickly; lines far apart mean gentle ground.

As a rough guide for a 1:25,000 map with 10-metre contours:

• 8 mm or more apart: gentler than about 1 in 20. Easy walking, the sort of lane you can chat on.
• Around 4 mm apart: roughly 1 in 10. A steady, noticeable pull that will slow you down.
• Around 2 mm apart: about 1 in 5. Properly steep — hands on knees if the path goes straight up.
• 1 mm or less: 1 in 2.5 or steeper. Expect steps, a scramble, or ground shown as crags. Treat it with respect.

Once you have walked a few of these gradients, the conversion becomes instinctive. You will find yourself glancing at a lane and thinking "that's a two-millimetre hill" without doing any arithmetic at all.

Counting the climb

Spacing gives you steepness; counting gives you total height gain. Find your starting height from a spot height or a numbered contour near the car park, then find the high point of the route — often a summit spot height or the highest closed contour ring. Subtract one from the other and you have your net ascent.

Be careful, though, because net ascent is not the same as total ascent. A rolling ridge route can gain 400 metres in total while only ever reaching 150 metres above its start. Every dip you descend has to be climbed again. If a route crosses several spurs, count the climbs, not just the summit.

Index contours help you count quickly: if every fifth line is thicker, you can hop between them in 50-metre steps rather than counting tens. On a long climb, counting "one, two, three, four — that's fifty" is a pleasantly distracting way to pass the time.

Turning contours into time and effort

Rough walking pace on good paths is around 4 kilometres per hour, a little faster on tarmac lanes and noticeably slower on tussocky moorland or through mud. Add time for the climbing: a common rule of thumb is an extra hour for every 600 metres of ascent.

In practical terms, that is about 10 to 15 minutes for every 100 metres of climb. So an 8-kilometre walk with 400 metres of ascent is roughly two hours of flat walking plus another 40 to 50 minutes of uphill effort, before you add stops for gates, stiles, photographs, a flask and a sandwich. Add generously if you are walking with children, carrying a full pack, or setting out in January when every field gate has a mud bath in front of it.

Choosing a kinder route

Contours are your best tool for route planning, because a bit of work at the kitchen table saves a lot of suffering on the day.

• Prefer one climb over three. A route that climbs once and descends once is far easier than one that nips up and down repeatedly, even if the total distance is the same.
• Watch the angle of crossing. If a footpath crosses contours at right angles, it is going straight up the fall line — the steepest possible line. If it crosses them at a shallow diagonal, it will feel far gentler.
• Look for a col. Where two summits meet, the contour lines pinch into a saddle shape. That gap is the lowest crossing point and almost always the sensible way over a ridge.
• Follow the valley shelf. Many country lanes and bridleways run along a contour, gaining height slowly as the valley falls away downstream. Those are the lanes that make for lovely, unhurried walking.

Reading valleys and spurs

The V shapes matter. In a valley, contours form a V that points uphill, upstream. On a spur or ridge, they form a V pointing downhill, out into the valley. This is a quick way to tell whether you are looking at a stream-bottom hollow — often wet, reedy and muddy — or a tongue of higher ground that will be drier underfoot.

It also tells you a lot about lanes. A lane tucked on the side of a valley, running parallel to the contours, will be a pleasant place to walk. A lane that crosses six contours in 300 metres will be short, steep and probably have a hairpin bend halfway up for very good reason.

What contours don't tell you

Contours are simplified. A 10-metre interval hides knolls, ditches, hummocks and small hollows, so a section of map that looks flat can still be tiring to cross. They also say nothing about gates, stiles, bogs, brambles, herd of cattle, or whether a footpath has been walked into a clear line or swallowed by June bracken. Dense contours beside a path might mean steps, or they might mean a rough scramble through heather.

Use contours to judge the shape and the effort of a route, then temper that with what you find on the ground. After a while you will find you can picture a walk from the lines alone — and that is when map reading stops being admin and becomes part of the pleasure of a day out.