Map Reading & Navigation – Part 2

We are now going to take the line, that the map is like a book that needs to be read, one stage further.  What we are going to do is plan a simple route (write a story) and then go for a walk to understand the story the map is telling you.  This is where you use a map to navigate and find out where you are.

Plan A Short Walk

One of the most important techniques of navigation and map reading is to be able to identify objects and landmarks as you progress through a walk.  Even when walking along a straight footpath, it is important to know where along that path you.  So, we are going to do a simple exercise, initially at home but then outdoors, to practice this technique.

Exercise:  I want you to plan a short route near to where you live and identify all the features and landmarks that are close to or cross your route.

Example: See the route that I have selected and the list of features that I would identify.

route

Starting from the west (left) and heading east, the key features that I would select are:

  1. Farm buildings to the left and right with a small road heading away to the left.
  2. Quarry access road on left
  3. Field boundary on the right with woods approximately 250m beyond.
  4. Field boundary to left followed by a second on the left.
  5. Field boundary on right with woods closing in.
  6. Slight left-hand turn in track followed by trackway heading away to the right as the woods close up to the route.
  7. Track continues with field to left and woods to the right.
  8. The meeting of 3 paths/tracks as small wood starts on the left
  9. Exiting small wood on left at junction of two paths, one to the left and one to the right.
  10. Route continues with woods on right and field on left.
  11. On left-hand side, concrete top to an underground reservoir.
  12. Route ends at junction between path to the right into the wood and a path to the left leading to a Trig Pillar.

I have selected a lot more features than would normally be necessary for such a short route.  But the point I am trying to make is that there are usually plenty of features to note both on the map and on the ground.

Exercise:  Once you have planned your route and noted the features, go for a walk along that route and identify the features on the ground.  You will soon realise that you will always know where you are along the route.

Relief and Contours

You will have noticed that the map is covered in faint brown lines that curl their way around the landscape.  These are contour lines, lines draw on a map connecting points of equal height above sea level.  On the 1:25000 scale map, contour lines are usually 5 metres apart. (This may change to 10 metres in mountainous areas).

contour lines

Contour lines are used to represent hills, valleys and slopes on a map and are very important features to understand.  They can offer up a lot of information such as the steeper the slope the closer together are the contours.  With practice you will soon be able to tell a hill from a valley or a col from a ridge.

concave convex

 

Although the contours are spaced 5 metres apart, only every fifth is annotated with the contour height, this line is also printed slightly bolder.  A good tip to remember is that the contour numbering always reads up hill.  So the top of the number is up hill.

Exercise: Take a map out to an area where there are hills and valleys and compare the contour lines on the map to what you see on the ground.  Look for hills and valleys, shallow and steep slopes.

Steepness

Identifying+slope+steepnessUnderstanding steepness is crucial to route planning and navigation.  As I have already said, the closer the contour lines are together, the steeper the slope.  This can be measured by comparing the vertical and horizontal components of the slope and presenting them as a percentage gradient (often used to denote steeps road i.e. 10% gradient).

Therefore a 30% gradient is a slope that rises by 30 units for every 100 horizontal units.  So, on your map all you have to do is count the number of contour lines in 1cm.

Example: Assuming you are using a 1:25,000 scale map

4 contour lines in 1cm (250m)

Therefore 16 contour lines in 4cm (1000m)

16 contour lines = 80m vertical (5m per contour)

This equates to 8m vertical per 100m horizontal or a gradient of 8%

Now whilst an understanding of steepness is very important, there is no requirement to do calculations each time you want to see how steep a slope is.  Instead, I recommend the ShavenRaspberry, or other similar, range of products, one of which is this slope calculator.

slope-angle-card-front

Before we leave contour lines, I just want to cover the foreshortening effect. Because a map is 2D slopes will appear shorter than they are.  This is important when calculating distance covered.  The Table demonstrates the consequence of the foreshortening effect.

Slope Angle  Additional Distance Travelled

10°     1.5%                                  40°      31%
20°      6%                                    50°      56%
30°      15%                                  60°      100%

The effect is slight on slopes that hill-walkers will use, it is still an extra distance that should be taken into consideration.

Pace Counting

When you are walking between two points where there are no obvious features or you are in poor visibility, it is important to have another means of calculating distance.  One of the most accurate techniques is Pace Counting.

The technique involves counting the number of paces from a starting point.  As each pace, in theory, should have the same distance, it is possible to relate the number of paces walked to a given distance over the ground.

Pace-notes-v2.jpg

However, not only does the length of a pace vary for each individual, it will also change as a result of variations in terrain and slope angle.  As a result, this technique is unique to each individual and can only be established by practice and experience.

Exercise: Count double paces (counting on the same foot each time) over a measured distance, such as 100m.  Do this for flat ground, varying slopes, different terrains.  Keep a permanent note of these with you at all times.

Pace-Calculator-version-2
fill in the blanks and keep with you as a guide.

Acquire some sprung toggles and attach them to piece of cord fixed to your rucksack.  Each time you reach the count for 100m, move a toggle to the end of the cord and start the count again from zero.  This way there is less risk of losing count!

Orange-Toggles-loop
Toggles supplied by ShavenRaspberry

In Map Reading & Navigation – Part 3, we will be introducing you to the compass, seeting a map, taking bearing and triangulating your position.

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