Grading a walk

So how difficult is the walk ?

An easy question to ask . . . and a difficult one to answer.

You will have noticed that all the walks offered by The Bentham Footpath Group are graded as Easy, Moderate or Challenging, and we define those descriptions based on a combination of the length of the walk and the total elevation gain, using this template:

Easy means . . .

  • less than 12 km in length and less than 700m total ascent
  • (less than 7.5 miles and less than 2300 ft total ascent)

Moderate means . . .

  • 12 – 15 km in length and less than 1000m total ascent
  • (7.5  –  9.3 miles and less than 3280 ft total ascent)

Challenging means . . .

  • More than 15 km in length OR more than 1000m total ascent
  • (more than 9.3 miles OR more than 3280 ft total ascent) 

This is useful: Some group members know that the challenging walks may be too much for them, and so can choose accordingly. But there’s still a problem – with just three broad categories there is still quite a range within each category. So, in order to help users drill down to a more accurate diagnosis of how challenging the walk might be, we introduce . . . 

Naismith Miles

William Wilson Naismith was a Scottish mountaineer and co-founder of the Scottish Mountaineering Club who coincidentally was a trained accountant. It is perhaps because of his accountancy training that he took a strong interest in devising a method to calculate how long a walk should take.

The original form of Naismith’s works was referred to as Naismith’s rule, and it stated . . . 

Allow one hour for every 3 miles forward plus an additional hour for every 2,000 feet of ascent.

So Naismith’s focus was on predicting time. This is certainly important when routes in the Scottish Highlands needed to be fitted into quite limited daylight hours, but our primary interest is in deciding how difficult the walk is – not just how long it will take. Enter Professor Philip Scarfe of Salford University who created a simple mathematical method to convert Naismith’s time into an equivalent distance. We refer to the result as “Naismith Miles”

The sciencey bit . . .

Scarfe rearranged Naismith’s formula to say . . .

equivalent distance = x + α·y           where:

x = horizontal distance
y = vertical distance
α is a constant usually referred to as Naismith’s number and is calculated  to be = 7.92 (3 mi / 2000 ft)

In plain English, this just means that 7.92 units of distance are equivalent to 1 unit of climb.

We round this up to 8 and calculate the number of Naismith Miles for every walk in the BFG collection

So how do I use it?

  • Go to the Search for Walks page.
  • Find the Search and Filter column on the right
  • Notice that the page is currently showing you ALL the BFG walks
  • Scroll down to the filter called “By Naismith Miles” – it looks like this —–>
  • Enter numbers in the lower and upper bounds, or drag the sliders to set your limits
  • Notice that the walks shown are now filtered to be between the Naismith Miles limits you have chosen
  • At this stage you will probably not have a good feel for where your personal limit is, so it might be wise to pick a route you know to be within your comfortable range and to check how many Naismith Miles that covers. Then pick walks close to that, extending your range gradually until you find a comfortable limit.
  • We hope this helps, but don’t forget, you still need to take account of weather and ground conditions in planning your walk.