The Basics of Navigation

Transcription

1 The Basics of Navigation Knowledge of map reading and the use of the compass is an indispensable skill of bushcraft. Without this skill, a walker is a passenger and mere follower on a trip. To become a good navigator takes experience, and lots of it, Navigation is about getting from one place to another. It is no more difficult than using the following few basic skills. Observation of your surroundings. Keeping track of features you pass, like hills and creek junctions. This is usually done mentally, though sometimes rough notes may help. Estimating how far you have travelled. Recognising important features when they are reached. People navigate using these skills all the time in the everyday world by figuring out where they are in relation to identifiable objects like roads, buildings, prominent landmarks (mountains, rivers), unique objects (the Sydney Harbour Bridge, Parliament House). The difference between everyday navigation and wilderness navigation is that instead of using objects like buildings, intersections and streets to get from place to place, bushwalkers tend to use natural features and landmarks. MAPS: Maps - these provide you with a bird's-eye view of the prominent features in a given area. Knowing how these features relate spatially to one another can help you: Types of maps Topographic maps - are generally made by government agencies, and are the most commonly used, since they give the best picture of the country. They are drawn from data obtained by aerial photography, which is very accurate providing the cartographer makes the correct interpretation. Unfortunately errors are sometimes made. Contour lines are used to indicate the shape and steepness/depth of hills and valleys. Many also include information about prominent man-made features like tracks, roads and bridges. Basics of Navigation.doc 8/05/2011 Page 1 of 7

2 Sketch maps - are usually produced by outdoors people for specific uses. Hills are often indicated pictorially, so accuracy is sometimes low. However, special details of tracks, passes, campsites and water availability are invaluable. Where possible, use both sketch and topographic maps together. Many sketch maps have become out-dated, due to changes in roads and tracks since they were drawn, but walking tips can still be relevant. Orthophoto maps - are similar to topographic maps, but are printed with an aerial photograph of the ground as a background to the other data. A fair idea is obtained of the pattern of vegetation, but other detail sometimes suffers. They are only available for limited areas. Contour lines are used. Basics of Navigation.doc 8/05/2011 Page 2 of 7

3 Map parts A map is a symbolic representation of the ground. To read a map requires knowledge of the symbols and how they are used. Scale: The relation between a length on a map and its corresponding distance on the ground is called the scale, given by a representative fraction. The most useful scales are 1:25 000, 1: and 1: Naturally there is less room for detail on a 1: map than there is in a 1: map, whilst the 1: scale can show very fine detail. 1:25000 this means that for every 1cm on map is equal to 250 m on ground 1: means that for every 1cm on map is equal to 500m on ground 1: means for every 1 cm on map 1000m/1km on ground 1:25000 is the best map for bushwalking it gives good detail, and shows a large enough area Contours: Hills and valleys are shown by contour lines, which join points of the same height. The vertical distance represented by two adjacent lines is called the contour interval. Thus, if you climb (or descend) a hill from one line on the map to the next, you will have moved vertically a distance equal to the contour interval: 10, 20 and 40 metres are typical values, depending on the map scale and steepness of the terrain. If the contour lines are 20 metre intervals, will you see on the map a rise less than 20m? The steepness of a given area on a topographic map is determined by how close together the contour lines are in that area. The closer the lines are together, the steeper the ground. Using the numeric information from the contours and the interval information from the bottom of the map, you can figure out: How high your current position is (assuming you know where you are on your map) How high any other specific point on the map is How steep the terrain is between where you are and where you want to go Basics of Navigation.doc 8/05/2011 Page 3 of 7

4 The Grid system: The entire globe is broken up into a grid system. The vertical lines that run north to south are called meridians of longitude and commence at 0 at Greenwich in London. These lines are not parallel. Those to the right of Greenwich are Longitude east, to left arelongitude west. The horizontal lines running around the globe are parallel and commence at the equator. These are called parallels of Latitude and commence at the equator. These are always marked North or South. Melbourne is E and S On a map the lines that run vertical are called easting; those horizontal are referred to as Northing. When reading a grid reference you do the easting first and then the Northing THE THREE NORTHS: North pointers: There are three Norths: true, magnetic and grid. For the area covered by a given map, the relationship between true, magnetic and grid north is usually shown by a diagram. The difference is referred to as magnetic declination. Basics of Navigation.doc 8/05/2011 Page 4 of 7

5 True North is the direction of the north geographic pole. And is the axis around which the earth spins. These are the Meridians. True North is therefore the direction form any point on the earth s surface to the North Pole. Magnetic North, is the point on the earth to which the compass points. It does not point to the North Pole. Its position varies each year slightly. You need to be aware of when the map is printed and how much it varies form year to year, and which direction. Grid North is the direction of grid lines: almost true North and South. North being the top of the map. These are the most convenient to use since grid lines are drawn on the map, and are parallel. Understanding the difference between the three Norths is essential when using both the map and the compass. Basics of Navigation.doc 8/05/2011 Page 5 of 7

6 The legend: Different maps provide different levels of this information. The shape of hills does not vary appreciably over decades, but map-making methods do. Unnatural features like roads and buildings can alter overnight. The date and maker of a map are important guides to its reliability. THE COMPASS A compass will not show you where to go, but it does point in a constant direction - magnetic north - providing there is nothing nearby to mislead it. Being magnetic, it must not be used too close to electric currents or magnetic and steel objects like knives, spectacle frames, fences, cars and corrugated steel sheds or tanks. While half a metre might he a safe distance to be away from a pocket knife, 10 or 20 m is probably better for a shed - not so much for its size, but rather because it is stationary and thus may have its own induced magnetism. There are a few locations where natural deposits of iron-rich rock play havoc, with compasses, such as Tabletop Mountain in the Snowy Mountains, but beware of imagining phantoms to explain away navigational puzzles - the fault is nearly always in the navigator! Parts of the compass: How to take a bearing: Orientate map Place compass on map lining up along the base plate edge, where you are and where you want to go Turn housing to line up orienting lines with grid lines Read bearing Minus variation (we are in the east) Put North in its house Follow direction using your mind map and map Basics of Navigation.doc 8/05/2011 Page 6 of 7

7 NAVIGATION HINTS: Spurs and ridge lines generally more open Gullies often thick Beware of relying on tracks for navigation Be sure of your position my matching the terrain Mental map making Collecting Features Estimating time to features Pacing Use you compass frequently Use your knowledge Refer to your topographic map frequently Maintain concentration or take a break Navigation tricks: Handrails Aiming off Contouring Implied knoll Parallel Error Descending a ridge (knowing when you are on a spur Attack points Catching features Basics of Navigation.doc 8/05/2011 Page 7 of 7