Distance and Time
Map Reading and Navigation
Course 1 · Chapter 6 · Distance and Time: How Far, and How Long?
A bearing tells you which way to go. It does not tell you when to stop looking for the next feature, or whether you can finish before dark. This chapter adds the other half: measuring distance on the map, judging it on the ground by counting paces, and turning distance and climbing into an estimate of how long a walk will take.
Measuring Distance on the Map
Chapter 1 introduced scale. Measure the line with a ruler or the edge of the compass baseplate, then multiply by the scale. On a 1:25,000 map, 1 cm is 250 m; on a 1:50,000 map, 1 cm is 500 m. Many baseplates have ruler marks already matched to these scales (called romer or scale edges), so you can read the ground distance straight off.
| Scale | 1 cm on the map | 4 cm on the map |
|---|---|---|
| 1:25,000 | 250 m | 1 km |
| 1:50,000 | 500 m | 2 km |
Straight lines and bendy ones
A ruler gives the straight-line distance. Paths wind, so the distance you actually walk is longer. For a curving route, lay a piece of string or thread along it, following every bend, then straighten the string against the scale. Another way is to break the route into short straight sections, measure each and add them up.
The division by 100 converts centimetres into metres, since the scale ratio is the same in any unit but you want the answer in metres.
Pacing
On the ground there is no ruler, so you count steps. A pace here means a double step: you count each time the same foot lands. Walk a known distance, for example a measured 100 m, count your paces and repeat a few times to get an average. Many people take roughly 60 to 70 double paces per 100 m on level ground (check), but the only figure that matters is your own.
Know your number
Measure it on flat, firm ground. Write the figure on your map case or the back of your compass.
It changes
Uphill, rough ground, heavy rucksack or tiredness all shorten your stride, so you take more paces per 100 m. Downhill often lengthens it.
Keep count
Count in hundreds. A pebble in the pocket or a bead on a cord (a pacing bead string) moves one place for every 100 m so you do not lose your place.
Best for short legs
Pacing is most useful over short distances in poor visibility, to find a feature on a bearing: walk the bearing for 400 m and you should be there.
Naismith's Rule
Distance alone is a poor guide to time, because climbing is slow. Naismith's rule is a simple formula for walking time on hill ground, usually credited to the Scottish mountaineer William Naismith in the 1890s (check). In metric form:
- Allow 1 hour for every 5 km walked (12 minutes per km).
- Add 10 minutes for every 100 m of ascent (1 minute per 10 m).
Descent is not counted in the basic rule. Adjustments for steep descents (check) exist, and so does a refinement by Tranter that allows for fitness and load, but the basic rule is where everyone starts. It is deliberately simple and is for a fit adult walking steadily with a light pack. Slower groups, bad ground, snow or darkness all add time.
Breaks, and Being Honest About the Answer
Naismith's rule gives moving time. Stops for food, photos, map checks and rests are extra. A common habit is to add around 5 minutes per hour for breaks, or to take a longer lunch stop and add it separately. Whichever you use, write down your allowance and keep to it.
Then check the estimate against your own pace. If a walk takes you a third longer than the rule says every time, use a multiplier of 1.3 in your planning. A rule of thumb you adjust is more useful than one you trust blindly. Chapter 7 uses these times to build a route card, and Chapter 9 uses them to decide when to turn back.
Common Mistakes
| Mistake | Fix |
|---|---|
| Measuring a winding path with a straight ruler | Follow the bends with string, or measure in short straight sections |
| Using the wrong scale factor (25,000 vs 50,000) | Check the scale in the margin before multiplying |
| Counting every step instead of every second step, or mixing them | Decide once and stick to it; calibrate with the same method |
| Forgetting the climb in Naismith's rule | Work out height gained from the contours and add 10 minutes per 100 m |
| Leaving out breaks | Add a fixed allowance per hour and plan to it |
| Assuming the rule fits everybody | Time a few real walks and apply your own multiplier |
Challenges
Convert these map measurements to ground distances: (a) 4.8 cm on a 1:25,000 map; (b) 6.4 cm on a 1:50,000 map; (c) 3.2 cm on a 1:25,000 map; (d) a piece of string laid along a winding path measures 22 cm on a 1:25,000 map. Which of these would you expect a ruler to underestimate, and why?
Using Naismith's rule (5 km/h plus 10 minutes per 100 m of ascent), find the time for: (a) 6 km with 300 m of ascent; (b) 10 km with 600 m of ascent; (c) 3.5 km with 150 m of ascent; (d) 8 km on level ground. Then, if you take 65 paces per 100 m, how far have you gone after 130 paces, and after 320 paces?
A walk has three legs: 2.0 km with 120 m of ascent, 1.5 km on the flat, and 3.5 km with 380 m of ascent. Write a short program or spreadsheet that gives the moving time for each leg, the total, and the total with a break allowance of 5 minutes per hour. State the total distance and ascent.
Quick Reference
- Map to ground: cm on map x scale / 100 = metres (1:25,000 gives 250 m per cm; 1:50,000 gives 500 m per cm)
- Winding routes: string along the bends, or short straight sections added together
- Pacing: know your own paces per 100 m; expect more paces uphill, on rough ground and when tired
- Naismith: 12 minutes per km, plus 10 minutes per 100 m climbed
- Breaks: extra; add an allowance such as 5 minutes per hour