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Tough, Light, Waterproof maps for Walking, Running & Cycling

Navigation blog

March 2020

March 2020

Contours - round or over, how to do a rough calculation
by Nigel Williams

This is sometimes referred to as Bob's Law in mountain marathon circles, but I have no idea who Bob is or was! But it gives us a rough rule of thumb. The premise is that roughly 100m of ascent equates to 1km on the flat.

Firstly, we need a way to quickly estimate how far it is to go from A to B via D compared to going over the end of the ridge A to B via C. A to B via D is approximately the combination of distances A to B (via C) 1km and C to D 0.6km = 1.6km.

Next, we count up the contours we cross going up. 8 = 120m of ascent on a Harvey map (15m contour interval). If we assume a walking speed of 4km per hour, 1.6km around the end of the ridge will take approximately 24 mins.

If we assume, according to Naismith's Rule, that we add 1 minute per 10m of ascent we get 12 minutes to add to the 15 minutes direct route over the ridge, giving a total of 27 minutes. So, in this example we might be quicker going around.

Of course, we all travel and manage hills at different speeds. Steepness and under foot conditions have a varying impact. If this example used a 10m interval for the 8 contours then it might be margin-ally quicker to go over.

On a mountain marathon the cunning route planner starting from A would have a check point at B, and then have the next check point back up on the ridge but several kilometres further along. So those that don't plan beyond the next check point risk climbing the hill twice instead of going around and then enduring the climb just once.

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December 2019

December 2019

Using the 3rd dimension for navigation
by Nigel Williams

The map and the compass are both 2 dimensional tools. Contours give us that 3rd dimension and an amazing amount of information both visually and kinesthetically, (through feeling): The closer the contours the steeper the ground, it is the changes that create significant navigation features.

Direction slope faces (aspect) - If I say my kitchen window has a southerly aspect I mean it faces south e.g. 180 degrees. Which direction a slope faces can be determined by taking a bearing directly looking down the slope. Place the compass on the map and move it around with the northing lines in the capsule and the N on the dial pointing to the top of the map and looking to see where the edge of the compass crosses the contour lines at right angles and pointing downhill. An altimeter would confirm which contour we might be on (1 in diagram).

A slope aspect is an invaluable relocation technique if seriously lost. It helps eliminate large swathes of the map where we cannot possibly be. If one is on a north facing slope (we may have several north facing slope options) we can't be anywhere that the contours indicate an east, south or west aspect.

Contours create line features such as ridges and valleys - but look more closely and even a change in slope steepness (break of slope) creates a line parallel to the contours which it is possible to see and follow. In fact it is possible to take a bearing similar to the slope aspect bearing but across the hill side. We can also see and follow the contour line indicating a change in steepness (2 in diagram).

A ridge or spur are linear features. We can therefore use aiming off techniques if there are changes in steepness along the ridge to find a specific point along it when approaching from a valley below.

Ticking off feature - we can keep track of our progress if we can match the ground we are travelling over to the map. Are we crossing contours at right angles or doing a rising traverse - does the ground flatten out briefly before a short steep climb across the contours? Changes in all 3 dimensions can be related to contours.

Catching feature - What does the ground do just beyond what you are aiming for. If you over shoot it is good to have something to stop you promptly and this could be a change in steepness or aspect, and can often be felt if not seen.

Combining an altimeter into our navigation is a powerful addition especially if one is any line feature. An altimeter will immediately tell us where we are along it and therefore our exact position.

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November 2019

November 2019

Contours - the 3rd Dimension
by Nigel Williams

Contours add at least 30% more information to the navigation decision making process, probably more than 60% in winter.

When we walk with a map we look to see what is around us and then look for it on the map or vice versa. Interpreting contours into something meaningful can seem a challenge but with a little practice it all starts to make sense. Contours are conceptual really and I think we often start with too big a landscape when teaching the subject. Class room models and orienteering scale maps with small hills, cols, spurs and valleys with varied contour spacing enable a better grasp of what they are all about. Look closely at the contour lines on the map - their spacing and therefore steepness of the ground is constantly changing.

There are little v shape bits, small spurs and gullies (often referred to re-entrants), sometimes just involving one or two contour lines. Streams and other features give us the clue as to which is a spur and which is a re-entrant. A circular contour line would indicates the top of a hill. These are sometimes referred to as the rule of Vs and Os.

The contour height numbers are of course a valuable clue as to what is up and down. If you are reading the numbers the right way up on the map you are effectively looking up the hill.
Unique to map information, contours provide a sensory experience as well as a visual one. You can feel ground shape and your relationship to it under your feet. It impacts ankle and leg joints, muscles (and even lungs). It affects our balance and we compensate for it. If we study the contours on our path the changes become tick off features or catching features as we go, eg the steepness of the ground is easing off. Instead of just knowing we are on the path we can identify where we are on it. The same principal works if we are walking on a bearing with a compass in poor visibility or at night.

Other sensory information helping us keep track of our direction of travel comes from things like changes to the feeling of the wind on our face, changing where the sun is in relation to our direction of travel, hearing running water - must be near a stream etc.

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July 2 2019

Contours Part 2 - further anecdotes of mapping elevation
by Nigel Williams

Between 1897 and 1906 bathymetric (and scientific) surveys of 562 Scottish freshwater lochs were carried out by Sir John Murray, an eminent oceanographer, and a large number of scientists (including his son who died in the process) using the same techniques as in the 1700s - a line from the bank to measure regular intervals and a plumb line for the depth. When the line from the bank got too heavy they resorted to 15 oar strokes between depth soundings. Bartholomew and Son mapped the 60,000 soundings into a series of 223 maps now kept in the National Library in Edinburgh. Modern soundings have proved them to be remarkably accurate; just 24m out for Loch Ness, for instance. Rather like the measurements taken of Schiehallion, this enabled calculations of volume etc to be made and was a world first survey of its kind.

From around 1865 to 1895 the British military in India were mapping the Himalayas with the help of Indian spies known as "Pundits" in the "Great Game" against the perceived Russian threat to the north - a brilliant piece of history made popular through Rudyard Kipling’s, Kim. They were intelligent men, often school teachers, and their work was celebrated by the RGS and a few even met Queen Victoria. The Pundits would attach themselves to trading caravans pretending to be merchants or Holy men. In addition to pacing using a set of rosary beads and a hidden compass in the top of a prayer wheel, altitude was measured secretly with a thermometer by recording the boiling point of water at natural stops in villages or the top of a pass. The last British spy master controlling the exploration and mapping apparently died in 1964 which adds a bit of perspective.

The 1930s re-triangulation of Great Britain developed the use of trig points. Initially there were over 6,500 but many have been lost to building development or have been removed. Around 25 years ago they became obsolete as satellites and GPS could now do the job. However, when Ordnance Survey announced they would remove them there was an outcry from the walking public and they were left in place to be adopted and maintained by local walking groups. I suspect if any organisation announced that they were going to erect thousands of concrete pillars on hill tops and other prominent places around the UK there would be a massive outcry against them.

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