Navigation Skills: Guaging Distance

When teaching navigation some of the biggest errors I see arise from people either walking too far or not far enough to their target. This blog describes non-GPS techniques, like pacing and timing. With practice these techniques can give you a high level of accuracy in gauging distance travelled.

Here’s are the bits of equipment you’ll need to practice these techniques:

  • a map
  • a stopwatch
  • a timing card
  • a compass (with a romer on it)

equipment

Measuring distances on a map

Before getting into the techniques for gauging how far you’ve walked you’ll need to be able to measure the distance on a map. Key to that is knowing what the scale of the map is. Here are some typical scales for UK maps.

Map 1cm measured on the map equals? 100m in the landscape equals
Ordnance Survey Landranger Maps 1:50,000 50,000cm in the landscape (that is 500m or 0.5km) 2mm measured on the map
Ordnance Survey Explorer Maps 1:25,000 25,000cm in the landscape (that is 250m or 0.25km) 4mm measured on the map
Harveys ‘British Mountain Maps’ 1:40,000 40,000cm in the landscape (that is 400m or 0.4km) 2.5mm measured on the map

To measure the distance between two points on a map you’ll either need to use a ruler (with millimeter increments) or compass romer. Make sure that you measure the route that you’ll walk, taking in any twists and turns along the way, rather than the straight line route.

romer

All hiking compasses made by silva and suunto have a ruler on them.  If you use a ruler you’ll need to convert millimeters you’ve measured into the equivalent distance in metres or kilometers in the landscape (see table above).

A compass romer is a scale ruler with 50m or 100m increments on the edge of your compass. A romer makes it easy to measure distance on your map. Most hiking compasses made by silva suunto have both a 1:50,000 and 1:25,000 romers on them. Some, like the Silva Type 4 Expedition compass, also have a 1:40,000 romer.

Once you’ve measured the distance on the map there are two principal ways of gauging distance on the ground: a timing method and a pacing method. Each of these methods is described below.

Timing Method

Timing methods use an estimation of how fast you are likely to walk. There are three types of timing method:

  • Horizontal speed
  • Rate of vertical ascent
  • Naismith’s rule

HORIZONTAL SPEED – This method is best suited to flat ground and gentle gradients. Look at the contour lines on the map over the route you intend to take. If they are relatively spaced out, indicating flat ground or gentle slopes, this is a good method to use. Consider how rough the terrain will be: boulderfields, boggy ground, snow, tussock grass and peat hags will significantly reduce your speed. Also consider how heavy your rucksack is, the weather and how fit the party is. All of these factors affect how fast you are likely to cover the distance.

Distance 5km per hour (this is the speed that most people will walk on flat level ground) 4km per hour (a heavy rucksack, gentle uphill slope, uneven ground or a less fit party may reduce your speed to 4km per hour) 3km per hour (tussock grass, boggy ground and rocky terrain are likely to significantly reduce your speed)
100m 1 min 12 seconds 1 min 30 seconds 2 minutes
300m 3 min 36 seconds 4 min 30 seconds 6 minutes
500m 6 minutes 7 min 30 seconds 10 minutes
1km 12 minutes 15 minutes 20 minutes

With practice you’ll get a feel for how fast you are likely to travel across different types of terrain and how things like weather, snow conditions, rucksack weight and party fitness will affect your speed.

Having made a guess of how fast your are likely to go, use the timing table (see above), together with the distance of your route – or leg – measured from your map, to work out a time. Now use your stopwatch to keep track of how long you have been walking.

TOP TIP: Measure out 100m on the ground – you could use a running tack or a gps device to do this – and practice walking the distance at different speeds. Try the same thing but on rough ground (e.g. rocky, boggy, tussock grass) and see how it slows your pace.

TOP TIP: Make sure you only time your moving or journeying time. If you stop to take a break pause your stopwatch and restart it when you begin moving again.

TOP TIP: During the course of your timed route – or leg – you can pace out and time 100m. If the 100m takes longer or quicker than you anticipated, recalculate your overall estimated time for the leg. 

TOP TIP: The timing table above can be printed off and laminated to make a timing card that you can refer when out walking. Doing speed time distance sums in your head when tired can be difficult!

TOP TIP: This method of timing can work well for downhills as well. Bear in mind however that steep descents or rough terrain on downhill sections can significantly reduce your speed.

RATE OF VERTICAL ASCENT – This method is best suited to uphills (i.e. slopes of between 10 and 40 degrees). Look at the contours on the map and consider where the uphill section begins and ends. Now work out what the height gain is for the uphill section in metres by counting the number of contour lines. Next make a guess of how quickly you are likely to ascend every 10m (this is your rate of vertical ascent). How steep the slope is, how rough the ground is underfoot, the weather, snow conditions, rucksack weight and party fitness all affect your rate of vertical ascent. You may find that your rate of vertical ascent will be quicker on steeper slopes than gentle slopes. For slopes of less than 10 degrees it may be more accurate to use the HORIZONTAL SPEED method at 3km per hour.

Height gain 1min per for every 10m ascent  1 min 15 seconds for every 10m ascent  1 min 30 seconds for every 10m ascent
100m 10 minutes 12 min 30 seconds 15 minutes
200m 20 minutes 25 minutes 30 minutes
300m 30 minutes 37 min 30 seconds 45 minutes
400m 40 minutes 50 minutes 1 hour

Like the HORIZONTAL SPEED method use a stop watch to time your ascent and progress uphill. With practice you’ll get a feel for how quickly you can gain height.

The rate of vertical ascent method was devised by Peter Cliff. You can read more about it in his book ‘Mountain Navigation‘.

TOP TIP: As you ascend a slope you can use an altimeter to check your rate of ascent. If you find you are quicker or slower than anticipated, recalculate the time for the whole leg. 

TOP TIP: When using this method, make sure you measure from the respective breaks in slope at the bottom and top of the slope. A break in slope is the point where the gradient of the slope changes; for example from a flat to steep slope, or steep slope to gentle slope. On the ascent of a hill, the gradient on the upper slopes can level off and plateau.   Make sure you stop at the point where the slope levels off. Subsequent sections of gentle slope or plateau en route to your hill summit should be treated as a separate leg using the HORIZONTAL METHOD.

NAISMITHS RULE – This method works best in when trying to estimate the time it may take to complete an entire route in hilly or mountainous terrain – including all the flat sections, gentle slopes, steep slopes and downhill sections. The method was devised by Willaim W. Naismith, a Scottish mountaineer, in 1892. To work out a time use the following formula:

Forumla Total distance @ 5km per hour + 1 minute for every 10m ascent
Example 1 12km total distance with 670m ascent = 2 hours 24 minutes + 67 minutes = 3 hours 31 minutes
Example 1 15.5km total distance with 1,370m ascent = 3 hours 6 minutes + 137 minutes = 5 hours 23 minutes

Add time for breaks to these totals to get an overall estimate for how long the hill day will be. Various modifications to the Naismith’s rule can be made; for example, changing the horizontal speed to 4km per hour for slower parties.

For micro-navigation, where a route is broken up into short legs, using a combination of the HORIZONTAL and RATE OF VERTICAL ASCENT methods works well.

Pacing Method

Counting your paces can be a really accurate way of gauging distance travelled, but it’s a technique that takes a lot of practice. The best way to get started is to go to a running track and walk 100m, counting every second footstep. Everyone’s pace count is different: some people take 50 double paces to cover 100m, some 75, it all depends on your stride length. When doing this for the first time try to walk in a relaxed way and not overstride.

The next step is to try the same thing off path, on moorland terrain. A GPS is really useful in measuring out 100m. Again, walk 100m, count every second step and see what your pace count is. It’s quite normal for your pace count to increase a little on uneven, rough, off path terrain.

A further progression is to try counting your paces on slopes of different gradients. First try a gentle slope (less than 10 degrees) and then a steeper slope (more than 20 degrees). Use a GPS to measure out 100m on a slope then walk it, counting every second step.  Very roughly you can expect your pace count to increase by 20% and 40% respectively on these slopes, but this very much personal to you and your stride pattern. My pace count over 100m is as follows.

Flat ground gentle slope (less than 10 degrees) steeper slope (more than 20 degrees)
63 double paces 76 double paces (about 20% more) 88 double paces (about 40% more)

As the gradient steepens you can expect your pace count to increase further. I find, however, that above a certain steepness (about 30%) the propensity to zig zag and the shortness of your stride makes pace counting inaccurate.

Once you’ve learnt your pace count over different terrain and on different gradients, measure the distance of your leg using a map to the nearest 50m. Let’s say that you intend to pace out 400m: rather than count 252 double paces (4 x 63 double paces) pace out 100m, then repeat three more times.

IMG_20190907_110555

TOP TIP: Pacing is most accurate over short legs. If you try to pace count 700m or more you may find errors creeping in.

TOP TIP: You can use different techniques to keep track of the number of 100m’s you’ve done: you could use a counter, you could move toggles on the lanyard of your compass or you could collect some stones and discard them as you tick off each 100m.

TOP TIP: Try to get used to what your stride length looks like and how many boot lengths you normally have between each footstep. If, for example, you have a space equivalent to one boot length between each of your footsteps and this reduces to half a boot length (over rough ground or up a slope) your pace count will be 33%. If you normally have two boot lengths between each footstep and this reduces to one boot length your pace count will increase by 50%.

This article forms part of a series about navigation skills:

If you would like to learn navigation skills why not attend one of our navigation courses, accredited by the National Navigation Award. We run beginner, intermediate and advanced courses (Bronze, Silver and Gold NNA Courses).

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2 thoughts on “Navigation Skills: Guaging Distance

  1. Pingback: Navigation Skills: Strategy – Aspen Outdoors Ltd

  2. Pingback: Navigation Glossary – Aspen Outdoors Ltd

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