Topography and Orienteering 1. Introduction Orienteering is about using a topographic map and compass to find points in the landscape. It is fun and challenging, as one would need to take reference to distance, terrain and direction, in order to find a location. In simple terms, orienteering talks about finding a direction or way. 2. Distance Measurement 2.1 Maps A topographic map is a mathematically determined presentation of a portion of the earth s surface. Symbols, lines, colours and form on the map depict the man-made and natural features on the real ground. All the representations on the map are drawn to scale, expressing the real features of the ground. They provide comprehensive information on the distances between location of ground features such as routes of travel and communication, populated places and extent of vegetation cover. It supplies information on the geographical situation of a particular area. It also indicates variation in landforms and heights of ground features. Map reading covers the ability to interpret the symbols (legends) shown on the map and to understand the information given in pictorial or written form, but it must also comprise a true understanding of the ground portrayed and an appreciation of the reality and value of the particular map being used. 2.2 Scale Maps carry scale to measure distances on the maps. They come in the form of ratio or graphic linear scale. 2.3 Measuring Straight Distance Fig. 1: Linear Map Scale Using a piece of paper, mark out the distance between the 2 points, use the graphic scale to get the actual distance on ground.
Using a ruler, measure the distance between 2 points, convert it to actual distance using the ratio given. 2.4 Measuring Curved Distance Consider the distance as several straight segments, using a piece of paper, mark out the distance between each segments, pivot the paper, turn the paper and mark out the next segment. Continue doing so until the end of the distance. Use the graphic scale to get the actual distance on the ground. Using a piece of thread, lay it along the route and mark both ends. Use a ruler and measure the distance and convert using linear scale. 2.5 Pacing Fig. 2: Scaling a road distance off a map
Pacing is used to determine distance traveled, it is generally based on 100m. There are 2 types of pacing, single step and double step. For single step pacing, you count on every stride whereas for double step pacing, you count on every alternate stride. Single step pacing is good for shorter distance as it is more accurate due to the fact that every stride is counted. However double step pacing is preferred for longer distance due as the number would be very big for long distance if single step pacing is to be used. 3. Shape of the Ground 3.1 Relief Relief is a general term applied to the shape of the ground on a vertical plane. The representation of relief on a map shows the heights and shapes of the ground above sea level. 3.2 Contours A contour is a line on the map joining points of equal height and the standard method of showing relief on topographical maps. Contouring combines an accurate indication of height with a good indication of shape, especially when used in conjunction with spot heights. Contours are shown at a regular vertical interval (i.e. difference in height between successive contours), which varies according to the scale of the map and to the type of country mapped. The contour interval is always stated in the lower margin of the map near the graphic scales. Contours are normally drawn as continuous lines. Every fourth or fifth contour is called an Index Contour, and is shown by a thicker line. Contour values are placed in breaks made in contour lines: they are placed so that they read the right way up when looking up the slope. The shape of a contour indicates the shape of the ground. When these contours are further apart, there is greater distance to travel to gain the height of the vertical interval between contours, and therefore the slope is gentler than when the contours are further apart. When the contours are an equal distance apart, the slope is uniform.
Fig. 3: Contours Contours are continuous. However far they run, they must in the end return to their starting points. The only exception is when a contour runs into a cliff where the slope is so vertical that there is no room in a plan view to show the contours separately. In such
case the cliff is usually shown by a symbol, and the contours run into it on either side where the slopes them to be shown. When the spacing of contours down a slope gets closer together at the bottom, the slope is convex, when the spacing of contours gets further apart at the bottom, the slope is concave. This gives long visibility. Irregular and closely spaced contours indicate rugged and broken slopes. Smooth contours indicate smooth slopes. Contours always run up rivers and streams. The sharper the angle at which the contours turn on the stream, the steeper the slopes on the sides. The correct interpretation of the shape of the ground from the contours requires practice and experience on the ground. It is essential to study the various features, comparing the map and the ground in each case. First concentrate on the major features (ridges, valleys, etc) and then study the minor features (variation in slope, etc). With practice it should be possible to build up a mental picture of the shape of the ground from the study of the map only, and then to prove it by checking on the ground. 4. Grid Reference A grid is a rectangular system of lines superimposed on a map, within which any point can be defined and located by reference to the lines enclosing the square within which the point falls. Each grid line has a number at the edge of the map. The vertical lines numbering from west to east are known as Eastings and the horizontal lines number from south to north are known as Northings. Grid references are always given with the easting value first followed by the northing value. When giving a grid reference to a square, the reference is always to the southwest corner (left-bottom) of the square. To provide a more accurate grid reference to a point of detail, it is necessary to break up the grid square shown on the map into ten subdivisions in each direction. The grid reference now will have an additional 2 digit to reflect the increase of accuracy. For example, if the current grid reference is 4 digit, dividing 1 grid box into 100 divisions will increase the grid reference to 6 digit, increase the accuracy. Should it be necessary to indicate a position even more accurately, the same method of estimation may be extended another stage by dividing each of the small squares again
into further tenths and by adding a fourth figure to each of the eastings and northings. The forth figure represents one hundredth of a unit. 5. Bearings A bearing is an angle, measured clockwise, from the zero degree line, The zero degree line is always North, unless some other zero line is stated. 5.1 Back Bearings A Bearing gives the direction of a line from the point of observation to a point, A of destination, B. Back bearing gives the direction of a line from B to A. Back bearing is the opposite of forward bearing. To obtain back bearing, subtract or add 180 degree to the forward bearing. If the forward bearing is less than 180 degree, add 180 degree to obtain the back bearing. If the forward bearing is more than 180 degree, subtract 180 degree to obtain the back bearing. 5.2 North There are three types of North: 1) True North 2) Grid/Map North 3) Magnetic North True North is the direction in which people assumed to be the North Pole which is the point where Earth s imaginary axis passes through. Grid/Map North is the northern direction of the north-south grid lines on a map. The grid lines on a map provide the most useful and normal reference for measuring bearings on a map: such bearings measured from the Grid/Map North are called grid/map bearings. These are the grid/map bearings most commonly used in map reading. Magnetic North is the direction in which a compass needle points when free from error or disturbance. This needle points to the magnetic pole which differs from the True North. Its position varies slightly from year to year. 6. Compass
The compass is a vital aid to orienteering. It can help you locate where you are on a map and assist you to find your way. 6.1 Parts of a Silva Compass Fig. 4: Parts of a Silva Compass 6.2 Taking a Map Bearing from a Map
Always set the Map by North first before taking any Map Bearing. To read a map bearing from A to B, place the compass with the longer side on the line AB and with the direction of travel arrow pointing towards B. Then turn the dial so that the orienting arrow on the housing are aligned with the magnetic needle and the orienteering lines are parallel to the eastings. The grid bearing of B from A is then read off at the point where the tail of the direction of travel arrow cuts the graduations on the circle. 6.3 Taking a Field bearing Hold the compass horizontally and point the direction of travel arrow at the object. While keeping the compass in this position, turn the dial so that the orienting arrow on the housing corresponds with the north end of the needle. The field bearing is then read off at the direction of travel arrow. 6.4 The Stick Shadow A stick shadow can give you accurate indication of direction. Push a stick vertically into the ground and mark where the tip of its shadow falls. After the shadow has moved several inches, mark the tip again. A line connecting the two marks will run east and west, east being in the direction of the second mark. Another line perpendicular to the first will run north and south. Fig. 5: Telling direction from a stick shadow
7. Walking Techniques 7.1 Man to Object Look straight ahead in the direction of set bearing. Pick a landmark at a reasonable distance away. Take the easiest route to the landmark without looking at the compass. On reaching the landmark, repeat sighting procedures and so on until you reach your destination. This technique is good for short distance and has lesser accuracy compared to Man to Man. This technique is normally used when there is shortage of manpower. 7.2 Man to Man Two people will be involved. The man at the back will make sure that they are traveling in the line of intended bearing/direction. The man in front will be responsible in keeping track of the distance/paces. In other words, the man in front is using the Man to Object technique. This technique breaks down the responsibility of keeping track of the bearing and direction of travel. This technique is good for longer distance and has more accuracy compared to Man to Object. This technique is normally used when there is enough manpower. 7.3 Side-stepping This is a movement to steer clear away from obstacles/restrictions on the line of travel. When met with obstacles in line of travel, one has to walk around the obstacle, but the number of paces taken to walk around the obstacle must be taken note of, so that a similar number of paces may be taken to return to the intended line of travel. 7.4 Detouring The principal is the same as side-stepping. However, detouring is used for bigger obstacle which would be very troublesome if one has to side-step to clear the obstacle. Instead, one will add or subtract 90 degrees from the original bearing and turn right or left respectively and walk as per normal. Similarly, the number of steps taken must be taken note of as the same number of steps will be needed to return to the original route. 8. Map Setting And Position Finding
Setting a map, means turning the map so that the details on the map correspond with the details on the ground. This is also called orienting the map. When in doubt about where you are, or in which direction you should turn, and when moving over a complex route, it is necessary to orientate the map to aid you in understanding the orientation of the ground. 8.1 Setting the Map by Inspection The simplest and the quickest provided you have some idea of your position. If you are on a straight road, line up the road on the map with the road on the ground, pointing it in the right direction: at a cross road, the map can be set similarly. If you are not on a road, or are on a road which is not straight and you cannot identify the bends, it is necessary to locate other objects such as a particular house, church, etc whose direction you can check in relation to your own approximate position. In open hilly ground, you may have to rely on the shape of the ground and on the corresponding positions of the contours. If you are on a ridge or spur, set the map so that the features correspond with the contours. Setting a map by this method is not precise, but the map can be set quickly and quite accurately enough for you to be sure of your direction. The features to be used will really have to depend on the situation. Normally roads are good indicators while landmarks are least reliable as the map might not be updated enough. 8.2 Setting the Map by North If you cannot immediately recognize sufficient details around you to enable you to set the map as described above, the simplest approximate method of setting is by the sun, if it is visible. To set the map more precisely, a compass must be used. With a compass, set the degree to zero, with the direction of travel arrow coinciding with the north direction of a grid line. Then rotate the map with the compass on it until the compass needle coincides with the north point on the dial. 9. Finding your Position
If you do not know your position, the first essential step is to orient the map by one of the methods described before. 9.1 Finding Position from Distant Detail (Resection) Resection is a skill to use when you know your own location on the ground but you are trying to find out your location on the map. In general, resection involves selecting landmarks to derive the area/spot of your location on the map. If there is no local detail, and if the contours are not sufficiently close or shaped to give you a reliable indication of position, your position can only be determined from distant objects such as hill tops, corners of woods, or other natural features. Select three points around you so that your position is within the triangle formed by the points. If you have a means of marking the line of sight from each point accurately on your map, while keep it correctly oriented, mark these lines on the map. If your map is correctly set, these lines will meet at a point which is your position, or at least they will make a small triangle within which your position falls. Check from a fourth point if available. Fig. 6: Resection Steps in Resection: 1) Orientate the map with regard to the magnetic north
2) Identify two or three known distant locations/landmarks on the ground and mark them on the map 3) Measure the field bearing to one of the known positions from your locations using a compass 4) Convert the field bearing to a map bearing 5) Convert the map bearing to a back bearing. Based on the back bearing, draw a line for the back bearing on the map from the known position back toward your unknown position. 6) Repeat steps 3,4 and 5 for a second position and a third position, or even more. 7) The intersection of the lines will be your own location on the map. 9.2 Finding the Position of a Distant Object (Intersection) It is to locate the position that is known on the map but unknown on the ground. Steps in Intersection: 1) Mark the known position in the map 2) Find the map bearing of the known position from 2 or 3 different positions that are easily accessible 3) Convert this map bearing of the 3 different positions into field bearing 4) Calculate the distance between the checkpoint and each position 5) From the first position, walk on the field bearing, according to the distance calculated 6) Repeat this procedure at each of the other positions 7) The 3 paths should intersect to give the position of the known positions on the map. The distance can be taken into consideration during practice or during execution to increase accuracy 10. Maintenance of Compass Do not bundle compasses together Do not swing compass about Do not place compass near metallic or magnetic objects Avoid dropping the compass Do not play around with the compass 11. Maintenance of Map Waterproofing a map: o Get a large zip-lock bag and some sturdy, waterproof tape o Wrap the map carefully in the plastic bag and seal it with the adhesive tape
o The map should fit exactly into the bag and not be allowed to slide within the bag. If a bag is bigger than the map is being used, sliding of the map can be avoided by further securing the excess plastic with the tape. Maps should be folded according to the grid lines It is necessary to fold a map because o It prevents a map from being crumpled in case of strong wind o It makes it more convenient for carrying o It allows the user to focus on the desired portion of the entire map 12. Setting Off 12. 1 Setting a Route To set a route, i.e. to establish a line of travel from one point to another point, employ the following procedure: 1) Orientate your map 2) Establish on the map where you are (by resection if necessary) 3) Establish on the map where you want yo go 4) Take a map bearing of where you want to go 5) Convert the map bearing to field bearing to obtain the direction of travel 6) Start walking in the direction of your objective, following the bearing established on the compass using the walking techniques. 12. 2 Map and Compass Tips At trail head, where you know your position, identify prominent landmarks and orient the map As you hike, pause frequently to consult the map or compass and establish your whereabouts. But do not stumble along looking at them. Each time you fix your location, check the map for features yet to come so you will recognize them. As you walk, watch for these features. 12.3 If you are Lost 1) Try to retrace your steps to the place where you knew where you are 2) If step 1 does not work, orientate your map. On the map, try to spot the last point where you confirmed your location 3) On the map, and in your surroundings, look for identifiable landmarks such as prominent peaks or ridges 4) If it still does not work, mark the spot where you are with a couple of rocks or a broken branch, so you will recognize home-base again
5) Then keeping your gear with you, walk in one direction for a hundred feet or so. If things do not look familiar, return to home-base and walk in another direction. 6) Continue to take straight-line excursions along the radius from home-base. More often than not, you will intercept the trail or spot familiar ground 7) If not, resign yourself to staying put for a while, perhaps overnight. Find a protected spot and make a shelter. If it is safe to do so, build a fire for warmth and for signal 8) Mark the area to help searches, using articles like clothing, a brightly coloured tarp or poncho 9) Ration your food