3 Factors That Can Skew Your Compass Reading:
>> Metal from a car, camera, drainage pipes, carabiners
>> Electrical fields from powerlines or a running car engine
>> Other magnetic forces, such as some lava beds, black sand, and half-finger gloves where magnets hold the mitten hood back
Recalibrate your altimeter every time you arrive at a known elevation, such as a pass or lake, since altimeter readings shift with any weather change that raises or lowers air pressure.
Keep Your GPS Locked On
Before entering thick woods, acquire satellites on your GPS, then pause for a new fix at each clearing or hilltop. To improve reception, hold the unit at eyelevel.
Use Common Sense
Your best navigation tools are your eyes and brain. If your map and compass place you on a steep slope but you’re standing on level ground, check your work.
Read Terrain on a Map
On a topographic map, the contour lines reveal an area’s three-dimensional landscape. Each line represents a specific elevation; the vertical change from one line to the next is a fixed value for that map (called the contour interval, it’s 40 feet on 7.5-minute USGS topos, the preferred map for backcountry navigation). Here’s how to identify key terrain features:
>> Cliffs Contour lines are very close together, almost touching.
>> Valleys and couloirs These have U-shaped contour lines, with the curve of the U pointing uphill; steep valleys or ravines resemble a V.
>> Summits Contour lines form concentric circles; the summit is the innermost and highest circle.
>> Flat or gently sloped areas Widely spaced contour lines
>> Passes/saddles Contour lines form an hourglass; the center of the hourglass will have higher lines on two sides (e.g., north and south of center) and lower lines on the opposite two sides (e.g., east and west of center).