Basics of Compass and Map Navigation
Every outdoors person should be as handy in the use of a map and compass as they are with a knife and fork. With a good map, and knowledge of its use, you can visualise the other side of a mountain, or what lies in the deepest valley. It is easy to procee
|Every outdoors person should be as handy in the use of a map and compass as they are with a knife and fork. With a good map, and knowledge of its use, you can visualise the other side of a mountain, or what lies in the deepest valley. It is easy to proceed confidently into unknown country and get to a destination without fuss or bother. 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, but just as with walking you can start easy and work up. Eventually you will develop a feel for terrain that will become second nature.|
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.
These observations are then related to the map, and only occasionally is the compass used as a check. The compass is simply a reference, which points, in a given direction. Although this review concentrates on bearings and other technicalities of the compass, it is better when starting to learn about navigation to concentrate on becoming familiar with interpreting maps - this can only be done by practice and plenty of time in the bush with map in hand.
Compass technicalities can be hard to learn from a book - it is better if you can get an expert to run you through them. Most of navigation is map reading - that is relating features shown symbolically on a piece of paper, to what you see around you. You are seeking to answer three fundamental questions: where am I, what direction do I take, and how far do I go?
The tools of the trade
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:
- Figure out where you are on your map simply by looking at the world around you.
- Figure out where your final destination is in relation to you, even if you can't see it (assuming you know your location on your map).
Compasses - these help you navigate more precisely from point to point. This can be extremely important in the wilderness, where even small mistakes can result in you walking right by your destination without seeing it.
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.
Sketch maps - are usually produced by outdoors people for specific uses and are only available for a limited number of popular areas. 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.
Other maps. There are other types of maps, including cadastral maps showing property boundaries. They are seldom of value for bush navigation. Some tourist maps and the like can be useful for planning trips or getting to the start of your walk.
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, 1:50 000 and 1: 1 00 000. Naturally there is less room for detail on a 1: 1 00 000 map than there is in a 1:50 000 map, whilst the 1:25 000 scale can show very fine detail. The 1:50 000 scale is a good compromise for most bush navigation, though you don't always have much choice. Large areas of remote Australia are only covered by the 100 000 series, which are not renowned for their accuracy on features like roads and tracks, although the topography is adequate.
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.
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
- 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 terrain will be.
Grid: The Australian map grid is a system of lines drawn over maps of the whole of Australia and is related to latitude and longitude. The lines are 1000 metres apart to scale. The grid is used to identify points on a map, somewhat like a city road map, except six figure numbers are used. Details of how to use these references are given on most maps that have the grid. You should be able to use grid references, as they are the main way of transferring route information from one person to another, as in route guides.
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.
- True north is the direction of the north geographic pole. The borders of most maps are true north and south, with north usually being at the top. A check should always be made - particularly of sketch maps.
- Magnetic north, to which compasses react, coincides with true north in Australia along only one line. The difference between the two is called the magnetic declination. (Hot linked)
- Grid north is the direction of grid lines: almost true north and south. The difference is usually small enough to be ignored for our purposes.
Conventional symbols: are fairly standard, but there are often variations and the legend should he checked. The non-topographic information that a map provides can be as crucial to navigation as the topographic information, especially for beginning bushwalkers. This additional information includes things like:
- The paths of access roads in the area
- The location of tracks and campsites
- Wilderness area boundaries
- The proximity of nearby towns and villages
Different maps provide different levels of this information.
Date and maker: 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.
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!
Insert diagram of example of compass
Principles of the compass
Compasses are basically designed to show you where north is in the real world. Knowing where north is allows you to identify all of the other directions in the ""compass rose"" (south, east, west etc.) as you travel and to head in those directions.
Insert diagram of example of bearing
Many compasses take this one step further, by allowing you to assign a specific numerical direction, called a ‘bearing’, to any direction in the full 360° circle around you. This means you can head toward a very specific spot, rather than simply heading on a more general heading (e.g. southwest).
To convert general compass directions into bearings, a compass has a special rotating bezel mounted around the outside edge of the compass needle. This bezel, which is divided into 360° usually in 2° to 5° increments°, measures the direction towards a given object in terms of an angle; specifically, the clockwise angle between a straight line pointing due north and a straight line pointing toward the object. This bezel allows you to express any specific direction as a number between 0 and 360.
When following a compass bearing from some feature, you may want to check back to that feature to see if you are on course, or you may wish to retrace your steps. The bearing in the reverse direction is called a back bearing and is simply 180' different from the forward bearing. The best method of obtaining a back bearing is - leaving the compass set at the forward bearing and held in front of you - simply turn around. There is no need to add or subtract 180': the south end of the compass needle now points to the north mark on the compass dial, and the travel arrow on the compass base points on the back bearing.
The importance of bearings
Following a bearing that is just one degree off can translate into a 25metre variance over a kilometre. This means that after a 10km walk, you may miss your target by over 200metres. In the bush, a few metres can mean the difference between spotting a track or creek and missing it completely.
Being able to measure directions in terms of specific compass bearings can also help in a number of critical situations.
- Knowing the bearing that the target you are heading for is on (river, house, campsite etc.), allows you to travel even if the weather closes in or night falls.
- Knowing the bearing allows you to keep you on track even if you have to detour around an object in your path (your compass will allow you to turn from your original course, get around the obstacle safely, then turn back and find your exact course again).
- Knowing how to take bearings can help you pinpoint your location on your map even if you are completely lost, using a technique called triangulation (discussed below).
Note: Knowing how to use a map and compass is very important for all bushwalkers. If you do get lost, or you have to cross an area of land without tracks, your map and compass may be the only tools that can get you back home safely.
Triangulation is one of the most common and most useful navigation techniques that use both a map and a compass. It is a simple procedure that, when done correctly, can pinpoint your exact position on your map even if you have no idea where you are.
Looking around you try to identify two unmistakable landmarks, say two peaks. If you take 2 accurate bearings on the two peaks, and draw a line on your map from each landmark along the bearings taken, your location will be where the two lines intersect. Triangulation is based on the principle that once you've taken a bearing on a visible landmark (i.e., established in what direction that landmark lies from your present position), you can logically assume that your position lies somewhere along a line drawn to that landmark along that bearing, the second bearing allows you to define the point.
Map and compass navigation works on the principle that you know one thing at all times and that is where north is. To find north, you simply look at where the red end of your compass needle is pointing.
The problem is that navigation is based on knowing where ""true north"" is, i.e. the North Pole. And unfortunately, that's not where compass needles really point. Compass needles actually point toward ""magnetic north,"" a point that is close to true north, but not right on top of it. And this is where ""declination"" comes in.
Declination is the angular difference between ‘true’ and ‘magnetic’ north. The tricky thing about declination is that this angle is different depending upon where you are standing in the world.
Declination is usually indicated diagrammatically with a series of arrows drawn on a map. These diagrams are often not to scale so always use the values, not the drawing to set your compass.
People navigate successfully with maps and compasses all the time, even though magnetic north and true north don't always line up. How? They simply figure out what the angle of declination is in their general area, and then make sure that they take that angle into account when they make their navigation calculations (basically, by adding or subtracting the angle of declination from the compass bearing numbers that they read off their compasses). Some compasses can be set so that they remain adjusted for an entire trip.