|Map and compass use for
hikers, cyclists, and others who venture outdoors
Use your compass and map to take a bearing
|Most people can
use a compass to
tell north from south. Few use it for much else. Yet the ability to take
a bearing on a known object, and to use that information as an aid in
determining your location, can save many hours of hiking or biking in
the wrong direction.
The technique described here may seem confusing as you read it. Try it, with a map and compass, at an outdoor location where you can follow the steps described. It will soon become second nature.
What are all those arrows on my compass?
1) The rectangular Base Plate (tinted light blue here; more often clear). It has a Direction of Travel Arrow running parallel to the long edge. The inside end of this arrow is referred to as the Index Line; you will have occasion to set the dial to this line or take readings from it.
2) The round Dial, with compass bearings on it (N,S,E,W, and numbers representing the 360 degrees of a circle). Inside the dial is an arrow which always points to the N (north) part of the dial. The various elements of the dial, which are connected and always move together, show in dark blue here. The outer ring is usually opaque, while the center circle is clear.
3) The Magnetic North Arrow inside, which points to magnetic north. (Red, with rare exceptions, is the north end.). Steel, iron, and electrical objects such as a battery-operated watch can throw it off, so keep your compass away from such item when you take a reading.
Other features: A small magnifying glass and a ruler or two are commonly included. Some compasses have a flip-up mirror that lets you take more accurate readings; that's a definite plus. Others have a control to adjust for magnetic north; some hikers find this superfluous, others like it.
Find your location on a known trail
However, you've used this map often enough to know that some trails shown have vanished without a trace. That first trail may be among the missing. So you can't just take your second right.
You've been hiking a while. The compass shows you're going south-southwest, as you should be, but you're worried that you may have passed your turn. How can you find out?
Take a bearing on a known landmark
Identify a specific feature, natural or artificial, that you can see in the distance, and that appears on the map. In this case, you can spot a church, down in the valley and across the river, which also appears on your map. A nearby peak, bridge, or river fork could also be a suitable landmark.
You'll get better results by using a landmark closer to you rather than farther, since increased distance will amplify any slight errors. The more perpendicular a landmark is to your direction of travel, the more helpful it will be.
Now use your compass to take a bearing on that landmark, based on the 360 degrees of a circle. North is 0 degrees, east is 90 degrees, and so on.
First, point the Direction of Travel arrow at the landmark. Next turn the dial until the Orienting Arrow (and the letter N) on the dial is aligned with the red Magnetic North Arrow. Now simply read your bearing at the Index Line. In this case, you find the church to be at a magnetic bearing of 105 degrees (between 120 and East, which is 90. On a real compass, you'll have more incremental markings.).
However, compasses point to magnetic north. True north may deviate from this by 10, 20, or more degrees. A good hiking map will usually indicate this deviation somewhere. If yours does not, then let's hope you thought to look it up beforehand! And while you're checking, look at the legend to see if the top of your map is true north. Usually it is, but not always.
If magnetic north is east of true north, then you need to add the deviation to your reading. (And -- you guessed it! -- if magnetic north is west of true north, then you need to subtract the deviation from your reading.) Assume we're hiking in central California where magnetic north is about 15 degrees east of true north. Add 15 + 105 to get the true bearing: 120 degrees.
Chart that bearing on your map
First rotate the compass dial so that the bearing of your landmark (120) is aligned with the arrow in the center of the rectangular base.
Next, maintain that setting as you place the compass on the map and rotate the whole thing until the orienting arrow in the center of the dial (the printed arrow, not the swinging magnetic arrow) points north on the map. Generally that means just aligning it with the north-south grid lines on the map.
And now, while keeping that arrow pointing north, slide the compass around until the long edge goes through the landmark.
Double-check that all three conditions are still met; it's easy for the dial to turn as you make the other adjustments.
Your location is somewhere along the compass edge that runs through the landmark. If you know you're on the trail, you just have to look to see where the compass edge crosses the trail; we've moved the Y there, to show your new position. (If the compass edge did not extend all the way to the trail, you'd need to make an imaginary extension.) Now you can see that you've passed the first trail turn-off but have not yet reached the next one. You can even estimate how far it is, and how long it will be before you should start watching for your turn.
Actual results may vary... ;-)
But in that case - or if you didn't know what trail you were on, but could identify a second landmark in a different direction - you could take a reading on both of them, and draw two lines on the map based on those bearings. The lines would intersect at your approximate location.Taking bearings on a known landmark is only one of many techniques for finding your way. We have another page with more advice about route-finding for hikers.
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