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Navigation blog

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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July 1 2019

July 1 2019

Contours Part 1 - some historical anecdotes
by Nigel Williams

I have just spent the past 4 days wandering around and up Schiehallion near Aberfeldy. It is here that contours were "invented" in 1774 by Charles Hutton where he was assisting the Astronomer Royal, Nevil Maskelyne, by gathering evidence to prove Newton’s theories of gravitation. He divided up the mountain into segments in order to calculate its weight which could then be scaled up to estimate the weight of the earth, its volume and its density. He plotted the heights of around 500 points on the mountain and essentially joined the dots thus creating contours.

More than 50 years earlier the concept of lines linking equal elevation values helped create underwater bathymetric charts such as the English Channel in 1737. In those days, with so many ships and men being lost at sea, mapping under water was probably perceived as a priority over land mapping. It is also a lot simpler to make a chart of a channel plotting depth readings using a plumb line, at a series of crossing points, than joining the dots running parallel to the shore giving the shape and steepness of the channel floor. Once on the beach though it was impossible to measure up the way with a plumb line. The first general map with contours appeared in 1791, the French engineer J.L. Dupain-Triel used a mix of contour lines at 20m intervals, hachures and spot heights on a map of France. Contours became established on Ordnance Survey maps in about 1843. All the contours on UK maps were originally drawn by hand from aerial photographs in the first half on the 1900s.

Harvey maps have added to the basic contour information with auxiliary or form line contours, height colouring and contour colouring (grey) to indicate underfoot conditions such as "predominantly rocky ground". They offer the best possible interpretation of the terrain as viewed by the hill walker, mountain biker, or runner on the ground.

Contours offer the most trustworthy information on maps and provide the 3rd dimension to help us make navigational decisions. Ignore contours and you are automatically cutting out around 30% of valuable information. In winter in the mountains they probably account for over 60% of the information and also have a safety element in terms of reading avalanche terrain.

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May 2019

May 2019

National Map Reading Week
by Nigel Williams

My first thought is why do we need a National Map Reading Week? Is it perhaps because there is no established teaching methodology for the subject in the UK. The focus of what is taught seems to be map reading based on numeracy and static plotting e.g. grid references and bearings. What we really need is a "National Navigation Week" and focus on the navigation skills required to walk with a map.
These skills are simple and don’t require numeracy. The skills required should match our walking experience. If that is achieved confidence levels will rise and perhaps more people will want to explore the countryside more often. Accept that everyone makes navigation errors but the skills improve with practice. Even if you are not responsible for navigating, have a map to hand and follow the progress identifying features and the distance covered.

Plan progressive walks
Build confidence with the map symbols and scale. Start by choosing routes that keep to large, simple handrail features e.g. tracks and paths. This will reduce the chance of navigation errors.

A second stage would be a mix of handrails and short cross country sections to another handrail (cutting corners) or big, obvious point feature (hill top). The third progression would be going cross country between smaller points features without handrails, probably requiring a good range of strategies and technical compass work and relocation skills.

Planning your route
Spend time studying the map and planning the route, to create a handrail to follow. Try to visualise the ground and know what to expect and see.

Timing a journey
Estimate the likely speed of travel over the day. Almost all walking maps are 1km across a grid square, 1.5km diagonally. We all walk at different speeds but estimating the day based on 3kph (20 minutes across a grid square) allows for regular stops. If walking uphill add a minute for each contour crossed going uphill. Treat downhill the same as being on the flat.

Setting up to navigate
Have the map and compass readily available and easy to use, ideally waterproof and in a pocket. Fold the map to the area being walked (about A5 size) and have the compass available to be held on the map with one hand so the two items are used as one.
Map and compass hung around the neck compromise the core skill of map setting. Be able to hold them in a comfortable position for ease of reading and so that they can be held up near arms length at eye level to accurately align features on the ground with the map and vice versa.

Re-tie the loop of cord that often comes with the compass as a single cord with one end tied to the compass and tie a loop big enough to thread the compass through at the other end. Attach to a belt loop or pocket zip.

Map setting
The single most important navigation skill is setting or orientating the map. Either by the features around you or by simply ensuring the red end of the compass needle points to the top of the map where the title is. The needle should be aligning accurately with the north south grid lines.

Look around and take in information. Think about the relationship between objects you see. This helps set the map and follow progress using tick off features.

Tick off features
Be curious to identify features on the map and on the ground whilst you are walking. Bends in the path, crossing streams, edge of woods, fence bends etc. Tick off features as you travel along the route.
Catching features
Recognise “Catching features” - identify things beyond the decision making points on your route. It is very easy if you don’t see what you expect, to keep on walking. A catching feature might be a stream crossing the path beyond the turning you should have taken. Using timing or pacing can also act as mental catching features.

Contours provide about a third of the map information available to the walker. They portray the shape of the terrain around you. Learn to include this third dimension when navigating.

As a back up to the map and compass, download a free app to your mobile phone that can give you a grid reference of your location (no signal required). It won’t drain the battery like digital mapping does and it is free. Also useful if you need help.

Practice for confidence
A wise navigator once said that "Navigation is 25% map work, 25% compass work and 50% confidence in the other two". The individual skills of navigation are easy and practice builds confidence.

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March 2019

March 2019

Global warming
by Nigel Williams

Today (Friday 15th March, 2019) there will be a "Global Climate Strike for the future - The beginning of great change". Greta Thunberg, the remarkable 16 year old Swedish schoolgirl, spoke at the Davos conference urging the world's most powerful, influential and wealthy people to act on climate change and the IPCC report is worth a read.

Predictions of warming are impacting, and will further impact, topography and mapping, so here is a parochial view of a few aspects that might affect the walker.

If temperatures rise by as much as 2 degrees over the next 30-50 years, sea levels around the UK could rise by over a metre.

The impact on mapping is obvious in Alpine and Arctic regions where glaciers and ice fields are shrinking and disappearing altogether. Around the UK the coastline would be the most obvious area to change as it is the lowest lying land.

On all Harvey maps, the High Water Mark or the high tide line is shown as a thin blue line. The line can be used as a safety aid for walkers to help them choose when to access coastal areas on long distance paths that integrate beach and coastal rock (such as the Anglesey Coastal Path – see image) or when to use an inland alternative route.

Mapping these lines has never been an easy task as it can often depend on the time of day the aerial photos used for photogrammetry were taken. However, there are several clues to assist in the interpretation of the images and photogrammetrists look for a mixture of natural signs to plot the high tide line. These can range from change in beach slope, drift lines on the beach and the change in colour of coastal rock. There is a significant skill involved in looking for these signs that requires years of practise. During the ground survey stage, these lines are checked and altered accordingly to give the clearest picture to the end user.

Should sea levels rise then not only would those lines need to be recalculated and re-drawn but every black dot (ground survey) spot height on our maps would need to be changed. Whilst contour lines would remain as they are all the contour numbering on every map would have to be adjusted.

Could Ben Vane become a Corbett? Will the Munro, Corbett, Donald and Marilyn tables all have to be re written? Could there be pre and post global warming rounds, the earlier ones being harder with cumulatively several hundred metres more height climbed?

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