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Introduction
This article was originally sourced from Scouting
Ireland CSI. The pictures have been modified to make them
legible and some into colour! Enjoy!
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Navigation
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Travelling through wild countryside is achieved by the use of a map
and a compass. The map conveys a detailed picture of the landscape
and terrain we are travelling across and the compass provides us
with a tool that will steer us in the correct direction. The secret
of good navigation is a good knowledge of map reading and
interpretation. The compass although important is secondary to good
map reading skills.
Understanding your map
The map is a representation of the landscape. It is produced from
satellite pictures and on the ground surveying. The map however is
only two dimensional therefore it must employ a method known as
contouring in order to show the rises and dents of the landscape. A
number of symbols are also used to establish such features such as
forests, churches, boggy ground, fences, train tracks etc. Roads and
tracks are marked on the map using a number of different coloured
lines and such methods as broken lines and chequered lines. Rivers
and lakes are marked in blue.
Scale
In order to draw a map of manageable size we use a process of
scaling to ensure the correct miniaturization of the landscape on
the map. Typical scales used are half inch to the mile, one inch to
the mile. In such a scaling system one inch on the map represents
one mile on the ground. Therefore the bigger the scale the more
information it is possible to draw onto the map. For walking
purposes you will be using the Discovery Series of maps which have a
scale of 1 : 50,000 or 2 centimetres to a kilometre ( one and a
quarter inches to a mile)
Grid lines
Overlaying all maps there is drawn a grid of light lines running
from top to bottom and side to side on the map. The purpose of this
grid is to allow us to identify every part of the map with a unique
number system ( grid reference). These grid lines which correspond
with the lines of longitude and latitude also enable us to identify
the north of the map and aid with compass alignment. You will notice
that each line is given a number, this will enable us to create the
grid reference number.
Grid Reference
A grid reference is a series of numbers (coordinates) which gives
us the exact location on a map. It is created by using the grid
lines which appear on all ordinance survey maps using the following
steps.
- Find your location on the map. If possible choose a
recognisable feature rather than a point in the middle of
nowhere.
- Find the grid letter on the national grid by looking at your
map. These are printed in blue and are large in size. Quote the
letter of the sector your position is in.
- Start at the bottom left hand side of the map and move across
the grid lines till you arrive at the grid line nearest your
location. The number of the line is the first two numbers of
your reference.
- You should then divide up the grid square into tenths. Half
way is .5, three quarter the way is .8 etc. State the location
of your position as a decimal. This number is the third number
of the reference.
- Repeat the same steps for the grid lines that cross the map
and this will give you the 3 figure reference for you location.
- You now have your six figure reference for your position.
A simple rule of thumb is the phrase that states - 'go in the
door and up the stairs'
Which means that if you visualise a door at the left hand side of
the map - then you go in the door (give the bottom line first) then
go up the stairs (give the side numbers next)
Aligning a map
In order to read a map correctly you must first align the map. This
is done by moving the map around until the map and the landscape
correspond. This is usually done by selecting a landmark or feature,
finding that landmark or feature on the map, then aligning the map
so that when you look at the map and then at the landmark their is
an imaginary line drawn between the two points. When your map is
correctly aligned you will be able to identify other features from
map to ground. The mountain peak on your left or the stream junction
on your right. If this exercise is done correctly by aligning your
map with two or three features rather than just one you can now
travel by using the map alone provided you establish correctly where
you are standing in relation to these features. As each feature or
new feature appears on the trail identify it on the map and re
establish your position.
Contours
Contours are the method used to convey the shape of the terrain you
are crossing. They are created by an imaginary line along which
every point is the same distance above sea level. These lines are
drawn at 10 metre intervals and allow us to see a representation of
the shape of a hill or mountain. By looking at your map you can
determine whether the mountain has a steep slope (contour lines
close together) or a gentle slope ( contour lines spread apart).
Contour lines are never or rarely circular in shape, because they
are plotting a set ground level they allow us to see the gentle
curves of a mountain as well as deep gullies. Practice on the ground
with your map will provide you with hands on experience, and over a
period of time you will get to know what variations of contour lines
mean and what they translate to in reality on the ground.
The Norths
A compass points to one north, your map is drawn with grid north,
and the stars point to true north. What is the difference and how
can you come to grips with then.
True North
True North is determined by sun readings and from the stars and is
the point we would call the north pole or very top of the earth
where all the lines of longitude converge.
Grid north
Map makers create a grid system around every country called the
National Grid. Each box on this grid has a letter. It is this letter
which we use to identify by means of a grid reference our position
on the grid. These grid lines are shown on our map and are numbered
thus allowing a grid reference to be created. As the position of
these grid lines are only slightly out of line with true north we
use them as our method of setting our compasses. So for our purposes
in Ireland and the British Isles Grid north and True north are the
same
Magnetic north
This is the north that is indicated on our compass. Magnetic north
is the location of a part of the earth which is magnetic and
attracts the needle of the compass. This north is located
approximately north of Canada. (8 degrees west of grid north)
How is each used
If you get lost or do not have a compass then you will relay on the
sun, stars and nature signs to show you the direction to follow. The
direction you will seek is true or celestial north. It is only a
general indicator and no fine navigation will be done by this
method. e.g. If you are lost and you know that from the last time
you looked at a map that a road was to the east of you. What you
would do is determine where north was by using the stars or sun and
create a compass in effect. If you are facing north then east is to
your right west is your left and south is to your back.
Grid north
Grid north as we have said is the map makers north. Therefore every
map is created with the top of the map being north, bottom south. If
you have your map folded up and you can read the writing on the map
( it is not upside down) it is turned in the right direction. This
is an important point to remember when it comes to taking a compass
bearing from your map (explained later)
Magnetic bearing
The magnetic north is the north that your compass needle will always
point to. This magnetic field is constantly moving so in Ireland it
moves by a number of degrees every couple of years. In Ireland the
current variation is 7 degrees west (1994) See the side panel of you
map to see what the current variation is. This means that your map
and your compass or out of line with each other. So in order to take
a directional bearing from the map and translate that to the compass
for you to follow you have to add on the variation of 7 degrees (
for convenience we use 8 degrees - 4 marks on the compass ). This
variation is different in every country so always check the side
panel of your map for variation particular to that location.
The Compass
The compass is an instrument that tells us where north is. This is
done by way of a magnetised needle that is allowed to float freely
within the instrument housing. Around the edge of the compass is
plotted a circle on which marking similar to that on a ruler are
inscribed. Each marking determines the number of degrees it is from
north to this point.
There are many compasses on sale from the simple floating needle
type to the more expensive plotting compasses. We will only be
concerning ourselves with one compass and that is the Silva Compass.
This is the best compass and only compass you should use for
navigational purposes on land.
The Silva Compass is made up of three parts - the needle, the
compass housing and the base plate. The needle is coloured red and
white and the red end points to north the white to the south. The
compass housing revolves and determines any desired bearing or
direction of travel. The base plate is used to indicate line of
travel.
How to use your compass
Your compass is a tool that is used in conjunction with your map. By
using the compass it is possible to navigate very precisely between
points on a map. Your compass can also be used to check your
position on the map and check the correctness of your line of
travel.
Taking a bearing
Place the compass on the map with the edge of the base plate along
the desired line of travel. The direction arrow on the compass
should point to the place you wish to go.
Move the compass housing until the north - south lines on the
transparent base of the compass housing are parallel with the grid
lines on the map. The north arrow on the compass housing should be
pointing north. You should be as accurate as possible when lining up
these lines as a movement each way will add or subtract degrees from
your final bearing and result in bad navigation and missing your
destination by hundreds of yards.
Lift up the compass from the map and read the bearing indicated on
the compass dial. Say this number to yourself then add on the
magnetic variation (e.g. Bearing is 92 degrees add on variation 8
degrees result 100 degrees) now move the compass housing to this
setting. It is a good practice to do bearings this way rather than
adding on by moving the compass housing immediately so that you do
not make a mistake. It is better to confirm in your mind what the
bearing is before you move the compass.
Your compass is now set. Hold the compass in your hand and move your
body around until the needle of the compass is correctly aligned
with the north - south markings on the housing. The direction of
travel arrow on the compass now points in the direction you need to
travel to your next destination.
This exercise is repeated from point to point as you travel on your
journey.
Following a bearing
You travel on a bearing by sighting a recognisable landmark along
its path and then travelling to that point and repeat until you
reach your destination. It is not advisable to follow your bearing
by looking at the compass and watching the movement of the needle.
As you walk you will have to move from side to side to avoid
obstacles so this method of following the bearing is discouraged in
favour of line of sight identification method.
However, if you find yourself in heavy fog or at night you will
use the method of looking at the compass to find your way. In fog or
at night you could use members of your party to line up on the
bearing under your direction and you then travel to these members.
This is a more accurate method than looking at the compass.
Back bearing
If you think you have erred from your line of travel you can check
your bearing by using a back bearing. To do this you turn around and
point the compass back to your last location. The white part of the
needle should now point north. If it is slightly out then it is
possible, by walking left or right until the needle lines up, to
correct your line of travel.
Finding your position on a map
To find your position an a map we use a process called resection.
This is preformed by plotting at least two points on the map to
determine your position.
First select a landmark that you can identify on the map and from
the position you are standing.
Point the compass at the landmark and move the housing until the
needle and north - south marking align. Read off the bearing on the
dial. Now subtract 8 degrees from that bearing. (e.g. bearing of 88
degrees less 8 degrees total 80 degrees). You then place the compass
on the map with the edge of the base plate on the symbol for
identifiable feature. Without adjusting the compass move the whole
compass round this point until north - south lines are parallel with
grid lines. If you have a pencil drawn a light line along the side
of the base plate. Your position is somewhere along this line.
You now select another feature which can be seen and identified from
your position and repeat the process. If possible choose a feature
which is nearly 90 degrees from your position. By doing this your
new line while precisely cross the line drawn from the other
feature. If the two points selected are two close to each other then
the lines will tend to merge and will result in a less accurate
determination of your position. Where the two lines cross in your
position.
Normally, two bearing are all that is required however, if you wish
you can use three to confirm exactly where you stand.
Nasmiths Rule
Nasmiths rule is a method of determining our speed of travel over
the countryside. It states that we walk at 3 miles per hour and that
we must add on to this calculation half an hour for every 1000 ft
climbed. This calculation can be converted into a metric measurement
thus - we walk at 5 kilometres per hour and allow 30 minutes for
every 300 meters climbed. For the purposes of calculating time
travelled with young people it is better to use a figure of 4 kms
per hour.
These calculations can be simplified
- 15 mins per 1 km
- 7.5 mins per half kilometre
- or in the height 1 minute for every 10 meters
These simplifications allow us to calculate with ease. Measure
the distance with the rule on your compass 2 centimetres = 1
kilometre = 15 mins travel time. Count the number of contour lines
you pass on your way up each contour line = 10 meters = 1 minute
extra to your travel time. You do not add on time if you are
descending a mountain or high ground. Be careful reading contour
lines on the map. You may have to calculate the height gained in
meters or feet depending on the map used. ( If you are using the
discovery series of maps it will be meters) Your start of position
maybe at the 150 meter line and you may travel through to the 250
meter line you have therefore climbed 100 meters meaning you have to
add on 10 minutes to your distance travelled time to give you your
correct arrival time.
4 kilometres per hour is a suggested average for hiking across easy
ground with a light pack. If you intend to carry heavy packs or if
you are travelling through rough countryside then you will have to
adjust this figure. The chart opposite will give you some guide, 2.5
kms per hour is the suggested figure for planning your route if you
are participating in a Mountain Pursuit Challenge. In determining
the correct speed of your Troop it is a good exercise to measure out
a set distance and time your Troop over this distance walking at an
average pace, with packs, etc.
This simply rule enable us to navigate across rough ground with
precision. We can also use this calculation to plan hikes and
adventures into wild country without leaving our sitting rooms.
Route Cards/Planners
Route cards are a device we use to plan our adventures across rough
countryside. The route card/planner tells us essential information
about our purposed route, number in the party, etc. The card also
serves as a safety device as we should leave a copy of the route
card with a responsible person who is not taking part in the hike or
trip. If an emergency arises then this person can advise the rescue
services of your route and aid your rescue. In preparing a route
card we break up our journey into convenient sections or 'legs'.
Each leg is then treated separately to calculate distances ,
bearings etc.
Filling out a route card
Each point of reference on the route card is identified with a grid
reference. So you will be travelling from grid reference to grid
reference rather than from the edge of the forest to the river. Grid
references give us precise position on the map whereas the edge of
the forest is open to interpretation. The direction of travel
between two points is determined by a compass bearing. These bearing
are obtained from your map ( don't forget to add on magnetic
variation) The next steps are to determine what distances you will
travel between points and the height gained and calculate the total
time for each leg of your journey. You will also need to add in such
things as - stopping to admire the scenery, and rest time. A general
rule is to allow 15 mins per hour. This 15 mins maybe spread over a
number of legs. In arriving at your total time you should also add
in time for lunch or meals as required.
You should take note of the actual time that it takes to complete
each section and put this figure down on your card. This information
will be useful if you decide to do the route again at a later stage.
It is also useful in determining your accuracy, which will improve
with practice.
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