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Navigation Methods

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Navigation Methods

Post  Warloque on Thu Nov 20, 2008 5:50 pm

Navigation Methods



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 insure the correct miniaturisation 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 (co-ordinates) 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.

1. Find your location on the map. If possible choose a recognisable feature rather than a point in the middle of nowhere.

2. 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.

3.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.

4. 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.

5. Repeat the same steps for the grid lines that cross the map and this will give you the 3 figure reference for you location.

6. 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.



Last edited by Warloque on Thu Nov 20, 2008 6:04 pm; edited 8 times in total
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Re: Navigation Methods

Post  Warloque on Thu Nov 20, 2008 5:50 pm

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 Baseplate Compass. This is the best compass and only compass you should use for navigational purposes on land.

The Baseplate 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.


Last edited by Warloque on Thu Nov 20, 2008 6:24 pm; edited 6 times in total
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Re: Navigation Methods

Post  Warloque on Thu Nov 20, 2008 5:57 pm

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.

Nature's Compasses
Finding our way using map and compass can be exciting but what if you had no map or compass and found yourself stranded in open countryside. Nature navigation relies on your skills of observation, through it you can find your way to safety.

Nature provides us with a variety of ways of discovering direction, the sun, the stars, trees and the wind. The simplest and most obvious way to find North is by the sun. At dawn it rises in the east, at mid day it is due south and in the evening it sets in the west.

Finding your way at night
Except for a few nights every month the moon, like the sun, can help give you direction. Because the moon reflects the suns light, the moon always points towards the sun, and thus even at night indicates the direction of the sun. Whether the moon is waxing or waning, an imaginary line through the horns of a crescent moon will always give you, approximately, a North South line.

The location of North can also be determined from the stars using the pole star. The 'Plough' Constellation is visible all year round as it moves around the pole star. On a clear night the pole star can be found by plotting a line through the 'pointers' the pole star can be found.



As with the sun and moon the stars also appear from the East and sink in the West. So, if a star rises you are facing East, if it descends you are facing West.


The wind
Almost every area has what is called a prevailing wind - that is a wind that blows longest and strongest from a particular direction.



Prevailing winds have their impact on trees, among other things the land. You can very often observe how trees in a given area have been influenced by a prevailing wind to lean in a particular direction. By observing the direction in which trees in an area are leaning, you can tell from which direction the local prevailing wind blows. If, say, the trees are leaning North - East you will find that the prevailing winds blows from the South west. There are but a few exceptions to this general rule - such as with the trees on some of our coastlines.
Nature also provides other wind - influenced indicators. Spiders, for example, do not construct their webs against the wind, so observation of the general direction in which spider webs are laid can be helpful.
Birds and insects almost always build their nests in positions that will protect then against the prevailing wind, so keep your eyes open.

Trees as indicators
We have talked about the prevailing wind effect on trees which causes them to lean in a particular direction. Further studies of trees however can reveal many ways in which a tree can indicate direction.
Concentrate your observations primarily on indigenous trees, because nature designed trees in different shapes, with the main object of enabling then to receive as much light as possible. Below we outline a number of pointers that will be useful. These observations are only generalisations. Trees are affected by many factors, and you should not jump to conclusions after studying a single trees only, but confirm your findings by observing several trees in the same vicinity.

Most trees tend to develop more foliage on the sunny side.

In many species the branches exposed to the arc of the sun and thus receiving more sunlight will tend to be branches that are more developed and that reach out southwards at an angle nearer the horizontal, while the branches on the Northern side lacking sunlight will tend to grow at a more acute upwards angle.

The tree trunk itself may lean sunwards, slightly. ( while the prevailing wind usually cause a tree to lean with the wind, the sun can also affect its angle)

Though not always, mosses and lichens will tend to grow on the North side of a tree trunk, rather than on the Southern, sun facing side. Note however that mosses and lichens are also affected by humidity - they flourish best where moisture is retained longer. You can also observe a green strip on the North side of wooden telephone poles and similar pole.

The bark on the North side will often be darker and more tightly grained than on the Southern sun facing side.

If the tree has been felled the rings on the stump will be spread further apart on the southern side.


Watch Methods






Shadow method

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