|
The map is the main item needed for navigation. There are several types of
map, however the ones recommended on this site are the Ordnance Survey (OS)
Outdoor Leisure and Landranger series. The Outdoor Leisure is a scale of
1:25,000 which covers most of the mountainous areas in the UK, whilst the
Landranger is a scale of 1:50,000 and covers all of the UK. Maps are
availablehe UK. Maps are available in laminated and non-laminated formats. If
you can afford to spend double the money on a laminated map it is well worth
while, since they last a lot longer when used in poor weather (which is when
they are most needed) and do not need a map case (which makes using the map
more difficult).
Whether you are using 1:50,000 or 1:25,000 a square on the grid will always
represent 1 km. This means that a diagonal will represent approx 1.5 km. This
allows easy estimation of distance on the ground. The map consists of a series
of squares such as those shown below. The numbers are used to give a grid
reference. We read along the bottom followed by the top, so that in this
example 2307 would refer to this 1km square area. This is not really
sufficiently accurate to pinpoint your position, so the square is divided into
100 smaller squares. Now each small square represents 100m square, and we have
therefore got more accuracy. We call the new grid reference a 6-figure grid
reference.
Examples:
The green circle is in 230070
The red circle is in 239073
The blue circle is in 234076
On the map itself we do not have the yellow lines. Instead we must either
estimate, or measure the tenths of the square. One way of doing this is to use
a roamer scale on the compass. This is usually found on compasses at the more
expensive end of the market. It is a scale at the edge of the compass. To use
it take the corner of the compass where the scale starts and place it on the
point which you need a grid reference for (we shall use the blue spot). Now
the number of lines will give the grid reference as 234076, as before. Note
you take the nearest line within the grid square. On the compass there may be
several roamer scales for various scale maps. It is important to use the
correct one.
We also use the map to allow us to interpret the aspect (slope) of the
ground. The contour is used to help with this. A contour is a line connecting
points of equal height. Usually the contours are at 10m intervals shown in
brown, with a thicker line marking 50m. Also spot heights are used to give the
height of a certain point. They are indicated by a brown dot. The height is
marked somewhere along the contour. When you look at the height the right way
up, you will be looking uphill.
The diagram shows a set off unlabelled contours. We will briefly use these
to describe the hill. At the edge of the grid square the contours are widely
spaced. This indicates that the ground is not too steep. As we go up the
contours get closer together, and we would find the ground getting steeper.
Then as they get further apart again the ground would be leveling off.
The diagram below shows the profile of the slope if we were walking along
the blue line. Each yellow line up represents 10m height. The width of the
profile would be 1km on the ground. A similar exercise can be carried out for
other directions. It should be noted that we do not know what happens between
the contours. It is possible that the ground might rise by 9m but this would
not be shown.
There are several contour features which you would expect to find in most
mountainous regions. It is a good idea to be able to recognize these. They are
1. The ridge where the ground reaches a high narrow point and drops off to the
left and right (eg Crib Goch).
2. The valley where the ground is relatively flat, and rises to the left and
the right (eg Nant Ffrancon).
3. The summit which is the example shown above.
These are other features which you will come to recognize with time. With
practice you will be able to relate the contours on the map to the ground and
decide what is suitable for you to walk over. Care needs to be taken when
switching between scales of map since the contours are closer together on the
1:50,000 because the square is smaller. The cartographer may sometimes miss
out the minor (10m) contours if the ground is too steep, and you should watch
out for this. Also note contours are rarely shown in quarries since the level
changes (eg Penrhyn Slate Quarries).
Back to navigation
|