A
compass is a essentially just a simple protractor. It measures angles. The basic
components of a compass are:
- Housing - This is the dial that can be turned to determine and set bearings
or directions.
- Bearing/Sighting Line - Like the sights on a gun, this line is used to point
the compass directly at a target.
- Needle - The needle is a thin strip of magnetic iron floating in an oil-filled
casing. The red tip will always point toward the magnetic north pole in the
northern hemisphere.
- Orienting Needle - The orienting needle is an arrow outline painted below
the needle. It is part of the housing, and rotates with the housing. The top
or front of the orienting needle is aligned with the north end of the needle
when navigating.
- Grid Lines - Grid lines are used to align north on a map. They should be
ignored for all other purposes.
Using a compass is much easier than most people realize. Remember a compass is
a very simple piece of equipment, and navigation is for the most part is a relatively
easy skill. If you are travelling towards a peak, or object that you can see in
the distance, but will soon lose sight of due to weather or terrain, you can use
the compass to continue in the right direction. While you can still see the target
use the sighting line to point the compass at the target. Without moving the compass,
rotate the housing until the orienting needle aligns with the needle. Now continue
on your way, traveling in a straight line to the target. When you lose sight of
the target the keep the needle aligned with the orienting needle, and follow the
direction of the sighting line. When the needle drifts outside the orienting needle,
stop, move the compass (the whole compass and yourself with it) until it is realigned.
Continue forward, adjusting when needed and eventually you will reach the target.
Congratulations! You are now shooting bearings and following bearings. Most, if
not all, compass work is a variation of this method.
Bearings
When you point the compass at a target and align the needle with the orienting
needle, you are taking a bearing.
The front or top bearing/sighting line will align with a number between 0
and 360. This is the angle of degrees the line you will be traveling is from
magnetic north. If it doesn’t make sense don’t worry, its not that important.
What is important is if the guide book you have been following says to travel
at a bearing of 291 degrees, you know to rotate the housing so that 291 lines
up with the front or top sighting line, move the compass and yourself until
the needle aligns with the orienting needle, and you follow the sighting lines.
Earth’s rotation and iron core creates a magnetic field much like giant magnet.
However the ends or poles of the magnet do not match the Earth’s geographic
poles. To make things worse, the magnetic pole tends to wander or drift, so
its location can change over time. Fortunately the drift is minor, and not significant
for wilderness navigation.
The difference between the true north pole and the magnetic north pole is easily
corrected. Simply add or subtract the difference between the two. For example
in the Canadian Rockies the magnetic north pole is about 20 degrees east of
the north pole. This is called magnetic declination. If you use your compass
to find a bearing of a mountain and it is 270 degrees, you have the magnetic
north bearing. Maps are made in relation to the true north pole unless otherwise
indicated. So the bearing on the compass is different than the indicated map
bearing. To correct take the 270 compass bearing and add 20 and you have 290,
the map bearing. Conversely a map bearing of 270 degrees must subtract the magnetic
declination to determine the compass bearing. In other words:
Compass Bearing + Magnetic Declination = Map Bearing.
Map Bearing - Magnetic Declination = Compass Bearing.
*These formulae only work west of Ontario
Maps are two dimensional representations of three dimensional features. Its a
flat drawing of a changing world. Topographical maps are the standard map for
most navigating.
Scale is a representation of the size of a feature on the map relative to the
size of the real thing. For example a lake measuring one centimetre on a map with
a scale of 1to 50,000, would represent an actual lake 50,000 centimetres or 0.5
kilometres wide. Whether you measure in inches, feet, centimetres, or thumb nails,
the relationship is still the same. When working with scales, the metric system
is definitely the one to use.)
Common Map Scales and Their Uses:
- 1:50,000 Used by hikers, ski tourers, backpackers, hunters on foot, Good
detail for travelling on foot in intricate terrain.
- 1:100,000 Used by hikers, ski tourers, and backpackers on longer trips in
more moderate terrain. Less detail but still useful for selecting appropriate
routes on longer trips.
- 1:250,000 An overview of large and extensive backcountry trips on foot or
ski, may be used for off road motorized travel , canoeists. Limited detail
with no information regarding mico-terrain features need for ground travel.
May be suitable for river or ocean trips with small craft
- 1:500,000 Paddlers traveling extended distances (200 kilometres or more),
general views of very large terrain features. Large areas covered with limited
detail
- 1:1,000,000 Overview maps of very large tours or expeditions. This is approaching
the detail of a large road map.
A contour line is continuous line of the same elevation around the edge of a feature.
Think of it as the edging trim along each layer of a wedding cake. Each line gives
an outline of what a feature looks like at regular intervals of elevation. The
closer together the lines are, the steeper the slope. For example the close gathering
of contour lines on Mt. Wrongagain represents a steep slope. The spread out contour
lines indicate a more gentle slope. The contour lines are at 100 foot intervals,
that is each line represents an outline of the mountain 100 feet higher than the
line below it. Contour intervals will vary with maps, and it is important to check
the interval to interpret the map.
To understand the shape of the mountain it is helpful to use the contour lines
to build an image of the feature, either in your mind or to draft out a profile
on paper. Here is a profile of Mt.Wrongagain.
The mountain has two peaks, with the higher summit on the left. The lower
slopes are moderate, becoming very steep towards the summits.
Because the contour lines are at 100 foot intervals we can only estimate what
the terrain between each contour looks like. An 80 foot cliff could easily hide
between contours and not be recorded on the map. With this in mind it is good
to remember that while these maps are generally very good, there is still room
for the odd surprise.
One of the most difficult things to interpret on a contour map is a sense
of elevation, ridges, and valleys. Here are a few tips. Water always flows down
through valleys or gullies, never ridges.
Creeks begin at higher elevations and flow down to lower elevations where
they join to form larger but fewer rivers. When contours form a bulge that points
from a lower elevation to a higher elevation, it is a gully, valley, or bowl.
When contours form a bulge from higher elevations to lower elevations it is
a ridge.
There are two methods recording a point on a map.
1. Grid system
The grid system is based on the light blue grids printed on most topographical
maps. On a 1:50,000 scale map, the grid is 1000 metres square. Along the outside
of the map on the top and bottom are a series of numbers called the Easting.
The first light blue number will be accumulated distance in metres from 0 on
the grid. On the Columbia Icefield map it begins at 467000 metres east. The
number increases by 1000 metres with each additional grid east. Mt. Snowdome
is located between 478000 and 47900 E. Using a ruler and knowing by the scale
that 2 millimetres equals 100 metres; the grid reference is 478400 E. The same
method is used to determine the northing, 5781750 N. This coordinate is expressed
in several ways:
478400 E, 5781750 N Full description
478400, 5781750 Easting first, Northing second
478400, 781750 The million metre reference is dropped from the northing (often
used in guide books)
The grid system is quick simple and very accurate.
2. Longitude and Latitude
This is the traditional system for global positioning. Longitude is a series
of imaginary lines radiating from the North and South poles. There are 360 degrees
of longitude. Latitude is a series of belts that circle the Earth. The equator
is 0 degrees, and the north pole is 90 degreees north latitude. The border between
western Canada and the United States is exactly 49 degrees north latitude. For
both latitude and longitude, every degree is broken down into 60 minutes. Each
minute is further broken down into 60 seconds. Longitude and latitude measurements
are located along side the grid measurements, but are printed in black. Longitude
is located at the top and bottom of the map. The longitude for Mt. Snowdome
is 117 degrees 18 minutes 55 seconds or 117018’55". Latitude is determined with
the scale on the side of the map; 52011’22" N. The N represents north, because
the same reference is used in the southern hemisphere. The north south designation
may be deleted from latitude if it is clearly understood that you are referring
to the northern hemisphere. If there is any doubt add the N designation to prevent
ending up somewhere in Chile. So Mt. Snowdome is located 117018’55" 52011’22"
N.
The grid system is generally much easier to use and is fairly standard for
guide books and reference points used by guides, foresters, and land rescues.
Most aircraft navigate with longitude and latitude and most gps units give coordinates
as longitude and latitude. This makes it important to know both systems. For
general travel and route finding the grid is probably a better system. If sending
word out for a rescue to park wardens, rangers, or guides the grid system is
generally the preferred system. When communicating directly to an aircraft give
longitude and latitude. If using a gps be prepared to use both systems.
On clear days with lots of reference points and a map it is fairly straight forward
to wander around and then use the map to orient yourself as needed. If the reference
points are few, and or the weather suddenly limits the view it is important to
know where you are. Lost is lost, and a compass and map will not find you. Know
where you are before you loose reference points or targets.
Lets assume you have set up camp on a high alpine meadow, and before settling
for the night you were able to mark the site on a map. Next morning the cloud
ceiling has dropped and you barely see the end of the tent. Somewhere in the
mist is a pass that will lead you back down to the valley, but where? Both the
camp and pass are on the map. Set the back edge of the compass on the camp and
the front edge to the center of the pass. Now align the orienting needle with
the north/south grid lines on the map. The bearing is 219. Map bearing -Magnetic
Declination = Compass Bearing. The map says that the magnetic declination is
20. So 219 - 20 = 199. Take down camp, set the compass at 199 degrees and confidently
lead the group to the pass.
If you do get lost with a map and compass all is not lost. You can still find
your way out with a little luck. Try to recall any reference points from the
last few minutes, hours, or days. Try and calculate roughly how far could you
have travelled in this time. Estimate the distance that you may have traveled
from the last reference point and mark this as a circle from that point on the
map. It is reasonable to assume that you are somewhere in this circle. Read
the contours within the circle and eliminate the places that you can’t be (glaciers,
lakes, cliffs, etc.). Now look at the possible areas that you can be. Are there
any large terrain features indicated on the map that you can travel to from
all possible locations ( such as large lakes, roads, well defined trails, railroad
tracks, power lines, rivers, etc.). Choose the most reasonable terrain feature,
take a general bearing with the compass and begin moving towards it.
Lets say you picked a river, sooner or later you will reach it. Now you know
that you are somewhere along this river. Now look around to see if there are
any reference points, if there are, you are no longer lost. If there are no
other reference points, look at the map and look for stream confluences, large
bends, cliff banks, any unique features along the river. Now decide whether
it is better to go upstream or downstream to find a reference point. This may
be a guess, but try to stack the odds in your favor as best you can. Eventually,
you will find a second reference point and know where you are.
When hopelessly lost, stop stay where you are, secure shelter, stay warm and
make your site as visible as possible for the searchers.
Previously incorrectly called triangulation, this method is used to locate your
position with two or more known points. Lets say you have just arrived at the
Highcountry Hilton, and want to mark the hut on your map. Find two known reference
points and take compass bearings off each one. Correct for magnetic deviation
(Compass Bearing + Magnetic Declination = Map Bearing) and draw the angle on the
map to the reference point. The compass makes and excellent protractor for this
exercise. Where the two lines cross is your present location.
If you are in new territory interpreting the contour lines will help you identify
features for references. Ideally you want reference points that are as close
to 900 apart as possible. This will give you a more accurate reading, but you
can further increase accuracy by choosing more than two reference points.
When travelling it can be useful to estimate your speed to help determine location.
If in an area with no reference points or limited visibility you can use the following
information to get an idea of your location.
Terrain Rate of Travel
| Gentle well maintained trails |
4-5 kilometres per hour |
| Rough backcountry trails |
3-4 kilometres per hour |
| Bushwhacking |
2 kilometres per hour |
| Poor weather/whiteout conditions |
2 kilometres per hour |
| For every 300m (1000 ft.) elevation gained |
add 1 hour |
This table is best used as a guide and modified as you become more familiar with
your own pace.
