How to Estimate Distance Travelled

Introduction

Land navigation is an important skill, especially for the military. The skill of navigation is inculcated from the start, beginning with recruit training, aka boot camp, and annual training.

There are many aspects to navigation, but an important one is to know how far you have travelled from your last known position. This can be achieved by estimating distance.

There are two tried and tested methods of estimating how far you have travelled:

  • Timing which is probably the easiest to perform, but it is often the least accurate.
  • Pacing is usually the most accurate but it can be laborious, especially over long distances.

When the weather and local conditions are difficult, it is often wise to use both methods concurrently.

Measuring the Distance

Before using either of the above methods, you will need to measure the distance on the map between your present location (Point A) and the target you are walking to (Point B).

Some people use the millimetres scale which runs alongside the compass base plate (left side of compass) while others prefer to use one of the romers (top right of picture).

Millimetres can sometimes be hard to distinguish, especially when there is rain or snow.

  • On a 1:50,000 scale map, one millimetre represents 50 metres on the ground (an easy mistake is to count one millimetre as 100 metres).
  • On a 1:25,000 scale map, one millimetre represents 25 metres on the ground.

Using the compass romer may be clearer, although some compasses do not have romers (military personnel should always purchase a compass with romers). Further, some compasses have removable scales for different maps.

Top tip: Use the correct romer for the map scale.

Timing

This is based on knowing the speed at which you are walking and keeping a note of when you left your last known point – especially important during reduced visibility, e.g. night-time.

Walking speed varies and is dependent on a range of factors including:

  • Fitness;
  • Weight carried;
  • Distance to travel;
  • Wind;
  • Conditions underfoot; and/or
  • Slope angle.

A formula for estimating the time required for a journey was published in 1892 by the renowned Scottish mountaineer, W.W. Naismith. There are numerous variations on this formula.

Useful estimates can be made without going into great detail and most people manage with just one or two versions of Naismith’s original calculations.

The simplest formula combines the horizontal distance with the height gained. For example, allow 5 kilometres per hour on the flat plus 10 minutes for every 100 metres height gain. Most reasonably fit people can maintain this speed throughout a day in the hills – provided there are not any particular difficulties – but remember that it does not allow for rests or stops.

‘Naismith’s’ is a valuable navigation aid and also a useful way of working out how long your entire route will take. To use this formula for short navigation legs, break it down to 1.2 minutes per 100 metres horizontal distance and 1 minute for every 10 metres of ascent.

However, you can only travel at the speed of the slowest person and therefore you may need to use a slower formula such as 4 kph which is calculated at 1.5 minutes per 100 metres.

When going gently downhill, it is best to ignore the height loss and just use the horizontal component of the formula. When descending steep ground which will slow your rate of travel, a rough estimate can be used. For example, allow 1 minute for every 30 metres of descent (although remember this is only an approximation).

A Timing Chart (Table 1 below) for the horizontal component can make the calculations easier – just remember to add 1 minute for every 10 metres of ascent.

Table 1: Timing Chart

Distance Travelled (Metres)5 KPH4 KPH3 KPH2 KPH
100012 min15 min20 min30 min
90011 min13.5 min18 min27 min
8009.5 min12 min16 min24 min
7008.5 min10.5 min14 min21 min
6007 min9 min12 min18 min
5006 min7.5 min10 min15 min
4005 min6 min8 min12 min
3003.5 min4.5 min6 min9 min
2002.5 min3 min4 min6 min
1001 min1.5 min2 min3 min
500.5 min0.75 min1 min1.5 min

Notes:

  • Timings have been rounded (up and down) to nearest minute or half minute.
  • Remember to add one (1) minute for every ten (10) metres of ascent.

Timing: Example

  • Distance:
    • Distance to be travelled: 850 metres.
    • Speed: 5 KPH for 100 metres = 1.2 minutes or 12.
    • 8.5 x 12 = 102 (or 10.2 minutes, round to 10 minutes).
  • Height Gain:
    • Height gain from Point A to Point B: 130 metres.
      • On an OS map (1:50,000 or 1:25,000) each contour is ten (10) metres.
      • Therefore 13 contours equals 130 metres.
      • Every fifth contour is a thick line (aka 50 metres).
    • One (1) minute for every ten (10) metres of ascent: 13 minutes.
    • 10 + 13 = 23 minutes.
  • Therefore, at 5 KPH, with a height gain of 130 metres, it will take approximately 23 minutes to travel 850 metres.

Pacing

Pacing is often more accurate than timing but it does require concentration.

An average stride takes about 60 double paces per hundred metres (a double pace is also known as a Roman Pace – hence the word “mile” which originated from a thousand Roman paces).

The Roman pace (Latin: passus) was a Roman unit of length. It was notionally the distance of a full stride from the position of one heel where it raised off of the ground to where it set down again at the end of the step: two steps, one by each foot.

You can determine your own individual pacing figure by measuring out 100 metres and then seeing how many double paces you take to cover the distance or you can do it on the hill between known points on relatively flat terrain.

You will need to alter the number of paces you take:

  • Going up-hill;
  • Going down-hill;
  • Walking on rough ground; or
  • In deep snow.

You can estimate how many extra paces you need to take to complete 100 metres at the end of every 60 double paces.

It is wise to measure the distance in hundreds of metres rather than by working out the total number of paces needed for a particular navigational leg.

For example, if the target is 450 metres away and your personal pacing figure is 62, then count 62 paces four times (which gives you 400 metres) and then add the final 31 paces (for the 50 metres).

It is useful to have a way of remembering how many hundreds of metres you have paced – it is easy to forget especially if someone asks you a question halfway through the leg.

Some compasses have a counter which fits on the side of the compass or you can use cord grips as counters on the compass lanyard.

Summary

Do not (always) expect your timing and pacing calculations to take you right to the spot you are heading for – look at the ground around you and compare it with the contours on the map.

Can you spot anything that does not fit in? If so, be tenacious about finding out why it does not fit. Look for other features which do make sense.

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