MAP & COMPASS

COMPASS: A good compass for backpacking is an orienteering model available at most outdoor stores. It should have a needle inside a clear rotating disk mounted atop a flat base plate. The plate should be engraved with a directional arrow (often called a direction of travel arrow). You should also have a "boxing arrow" or "boxing brackets" inside the disk that turns with the disk. The disk is divided into directions: north, south, east and west. Each direction is assigned a set number of degrees, 360 in all. 0 (& 360) degrees is north, 90 is east, 180 is south, and 270 is west. Any direction can be indicated by degrees. For example, 95 degrees is just south of straight east and 315 degrees is halfway between west and north. One end of the needle inside the disk is magnetized. It is usually red in color and is attracted toward magnetic north (which is located about a thousand miles to the south of true north in the Canadian Arctic). The difference between true and magnetic north is known as declination. This declination changes for each area and is usually shown or listed at the bottom of the map.

 

Map: Maps are drawn according to true north and so your map and compass must be oriented together taking into account the declination for your area. A good map for backpacking is a topographical map with 40 foot differences in the contour lines. A good base map to use is the 7.5 minutes series map available from the U.S. Geological Survey. These, and others can be obtained at most good outdoor stores.

Using the Map and Compass Together

Orienting the Map

1) Know the declination for your area. Usually found at the bottom of the map. Oregon, for example is usually between 18-21 degrees east declination. That is the needle in the compass points 18-21 degrees east of true north.

2) Align the direction of travel arrow on the compass base plate with 0 degrees.

3) Now set the proper declination by rotating the disk to the declination for your area. For example in a part of Oregon with a declination of 20 degrees east you would turn the disk to the east (right) 20 degrees. The direction of travel arrow on the base plate should now be aligned with 340 degrees. (If you had a west declination it would be just the opposite.)

4) Next align the long edge of the base plate of the compass next to the border of the map that shows a true north-south line (usually the edge of the map is best).

5) Now carefully rotate the map with your compass on it until the red magnetic north needle lines up inside the boxing arrow (or brackets) inside the disk. The edge of the base plate of the compass should still be aligned with the north-south grid line on the map. This is called "boxing the arrow." Your map is now properly oriented to your actual position.

From Map to Field

To travel cross country to another destination on the map do the following.

1) Orient the map (steps 1-5 above).

2) Keeping the map oriented (this is crucial), line the long edge of the base plate of your compass up between the point where you are on the map to your destination. Your direction of travel arrow should be pointed at your objective.

3) Holding the base plate firm on that line, rotate the disk until your boxing arrow (or brackets) are aligned with the magnetic north needle (in other words box the arrow). The degrees that are in alignment with your direction of travel arrow is your compass heading or bearing.

4) Stand with your direction of travel arrow pointed directly away from you to the front. Holding your compass in that position turn your whole body until the magnetic north arrow is boxed.

5) Sight a prominent landmark on the bearing of your direction of travel arrow. Walk to that land mark and repeat steps 4 and 5 over again until you reach your destination. Make sure you are following the same compass degree bearing each time.

From Field to Map

1) Orient the map (steps 1-5 under Orienting the Map above).

2) Take a bearing on a prominent land mark by pointing the direction of travel arrow at it and turning the disk until you have "boxed the needle."

3) Lay the straight edge of the compass against your location on the map (keeping the map oriented at the same time). Now, keeping the edge on your location, turn the whole compass (not just the disk) until you have "boxed the needle." You can now give anyone else who is at your location a compass bearing to that land mark.

Finding Your Location

1) Orient the map (steps 1-5 under Orienting the Map above).

2) Take a bearing on a prominent land mark by pointing the direction of travel arrow at it and turning the disk until you have "boxed the needle."

3) Lay the straight edge of the compass against your location on the map (keeping the map oriented at the same time). Now, keeping the edge on your location, turn the whole compass (not just the disk) until you have "boxed the needle." Draw a line along the straight edge of your compass. You are somewhere on that line.

4) Repeat step 3 with another land mark. You are where the first and second lines intersect. *** Note: These directions are not for a "set and forget" compass that allows for a semi-permenent setting of declination. ***