Using a compass as a navigation tool
A compass is a device that shows the user magnetic north. Contrary to popular belief, it doesn’t instantly tell you where you are! Rather, it’s a tool that bushwalkers use in combination with a map and the landscape to help figure out where they are.
Using an altimeter as a navigation tool
An altimeter is a tool that measures altitude above a reference point. It works by detecting small changes in atmospheric pressure, and bushwalkers can use a hand-held or wrist-mounted device.
Knowing altitude can help to verify the user’s location, particularly on long uphill sections. When used conjunction with a topographic map, a barometric altimeter is often more accurate than a GPS unit, which is susceptible to failure from satellites dropping in an out of availability and being wildly inaccurate when all available satellites are near the horizon.
Since barometric pressure is affected by weather and changes in weather, bushwalkers need to recalibrate the device periodically at a known location (e.g. trail junction, hill).
A description of the basic parts of a compass
There are many different types of compasses, but for bushwalking, it’s important to get a unit that can reliably measure bearings and help the user determine their travel route.
While all compasses are made up of the same general anatomy – a baseplate with arrows in the direction of travel, a rotating bezel with degrees markings, and a magnetic needle held within a housing unit with orienting lines on it – compasses also have a number of additional features like mirrors that may be appealing to some users.
Beware of cheap substitutes like compasses on keyrings and toy units. Spend the money for something that is lightweight, compact and reliable.
Basic Features:
1 Baseplate: The transparent panel on the base of the compass. Usually with ‘direction of travel arrow’ for orientation and ruler markings for calculating distances. The direction of travel arrow points in the direction you need to travel after setting a bearing.
2 Azimuth ring/rotating bezel: This rotating bezel has degrees markings from 0 to 359° around the outer edge, and encircles the needle capsule. The finer the scale, the more precise the navigation can be.
3 Magnetised needle: A black and red needle usually suspended in a damping fluid to help steady the movement. The needle spins freely on a mid-axis and the red end settles pointing towards the north magnetic pole.
4 Needle housing with orienting lines and arrow: Needle housing contains magnetised needle and damping fluid. It has orienting lines that can be aligned with the vertical grid lines on a map.
The orienting arrow is aligned with 0° or North on the housing.
5 Index line: The index line is an extension of the direction of travel line. It is fixed and marks any bearing that has been set by rotating the compass housing.
Additional:
6 Magnifying glass: for more detailed reading of map features
7 Declination adjustment: Some compasses have a declination adjustment feature where it’s possible to adjust the “declination” (ie. the difference between true north and magnetic) to match the area you are walking in. Thus, for every measurement, you don’t need to account for declination, rather instead, it’s taken into account for you. This works well if you are regularly using your compass in one area, and only need to reset it when you travel to a new area.
8 Sighting mirror: Can be helpful to aim more precisely for a distant landmark, especially in open terrain. Mirror can also double as an emergency aid for signally.
9 Global needle: Standard compasses only work in one hemisphere, so they are either northern or southern hemisphere specific. More expensive models can work in both hemispheres and therefore function well worldwide.
How to use a compass
Compasses have a small magnetic needle suspended in fluid that rotates freely around a fixed axis until it settles pointing towards magnetic north.
Bushwalkers can use a compass in two directions: (i) to read a bearing off a map and applying that to real life, or (ii) to read a real life bearing and apply that back to the map. In practical terms, this means that a bushwalker can use a compass to determine the direction or bearing from A to B from a map, then follow that bearing in real life. Alternatively, they can take a reading in real life and put it back on the map to help figure out where they are.
A compass enables the user to orientate the map in the direction of sight, helping the user to match map features with the physical surroundings. A compass bearing of a road direction, a creek direction, the orientation of a set of powerlines can also help bushwalkers to determine where they are on the map.
However, compasses do have their flaws. Since they rely on the earth’s magnetic field to align, any strong metal object or magnetic substance nearby can send the needle haywire. For example, metal implants in packs, clothing and phones. A common mistake is to set the map up on the bonnet of the car, but the compass needle will not point north.
In some parts of the world, the ground has high metallic content. Compasses are completely useless in these areas as the compass needle never points north.
Switching between hemispheres is another common problem with compasses. A northern hemisphere compass doesn’t work in the southern hemisphere and vice versa (unless you have a special compass that can do both).
And once the fluid around the needle gets a bubble in it or leaks, the game is over. The compass is unlikely to be accurate or work ever again. Unfortunately, it’s a common problem when traveling.
Users also have to be aware of magnetic variations and how far off north they are at any given time. The adjustment introduces another degree of human error into the situation.
All that said, people do love compasses. They’re something most people are comfortable with and used to. Just be aware of some of the issues around using them. Don’t forget to fasten your compass securely to your map case or neck so you don’t lose it!
Using a GPS, smartphone or tablet as a navigation tool
A GPS navigation device gives the user their location anywhere on earth. GPS stands for Global Positioning System, a space-based navigation system that uses satellites to identify a location. As long as the device has an unobstructed line of sight to four or more GPS satellites, it’s accuracy is within 20m, more than adequate for all on-track bushwalking needs.
GPS technology is now so cheap that most smartphones and tablets have a GPS chip that tells the user where they are. Providing suitable maps are loaded, a smartphone or tablet can be as useful as a conventional GPS unit. Both can identify your location with up to 20m accuracy. But even if no maps are loaded, a GPS unit, smartphone or tablet can still inform the user of their location coordinates. The user then has to use the correct datum and projection to be able to translate coordinate positions between the device and a physical map.
CAUTION: a GPS unit only gives location information. Users must still be able to plan and follow a route, which requires map reading skills.
Knowing location information is useful, but only one component of navigation. It’s no use knowing that your location if you can’t then use that information to get to your destination. Often, going directly from A to B in a straight line is not the best way, or worse, there’s a massive cliff in between. Route planning is about determining the best way to traverse the landscape, and navigation is about executing that plan.
Most GPS units are reasonably shock-proof and are waterproof at the very least for incidental exposure to water of up to 1 meter for up to 30 minutes. For smartphones, it’s possible to buy waterproof and shockproof cases, a good idea on any bushwalk. A waterproof case means you can also use the device in the rain.
However, just like any tool, GPS technology can fail! For example, the GPS unit might jam up, the batteries could run out, the unit could get dropped, or water gets inside the electronics. On a bigger scale, satellites can drop out or become wildly inaccurate if their position is near the horizon relative to you. A GPS will not work if it doesn’t have an unobstructed line of sight to four or more GPS satellites. For example, at the base of cliffs a GPS will give terrible results, and in dense forest the signal may be faint.
So that’s why it’s a good idea to carry backups. Often, a GPS user will also take a compass as a backup. Likewise, compass users will often bring a GPS unit as their backup.
