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Backpacker Magazine – June 2012
Master Class: Find Yourself on a Map
The best way to avoid getting lost? Always know your location. Study up on these key techniques for identifying terrain features, translating GPS data to a map, and triangulating your position.
(Photo by: Glenn Randall)
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Tags:
- Navigation |
- Skills |
3. ADVANCED
Skill: Triangulate with two lines.
If you are traveling along a known linear feature—like a river, mapped trail, ridgeline, or road—you can skip a step when triangulating your location. Shoot two bearings, translate them to your map, and use the known feature as your third point of reference. Your location is where the two bearings intersect the linear feature.
Adjust for Declination
Navigate accurately over distances.
Maps are oriented to true north, but compasses point to magnetic north. The discrepancy is called magnetic declination, and the farther east or west you get from the 0-degree line, the greater the impact on navigation. If you don’t correct for it (many hikers don’t), a 10-degree offset, like the one affecting parts of Colorado and Pennsylvania, could equate to a 1.7-mile error over 10 miles of off-trail hiking. Calculate your area’s declination with NOAA’s National Geophysical Data Center (ngdc.noaa.gov), or by referencing your map’s declination diagram (in the margin). Then correct for it:
>> Automatic Set your compass’s adjustable declination and program your GPS to display true north bearings.
>> Manual Shoot bearings with a non-adjusted compass. Add (for east) or subtract (for west) your area’s declination before translating the bearings to a map. Click here to learn more.
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READERS COMMENTS
Knowing your location on a map is one way to not-get-lost but sometimes getting lost can be easier than staying found and that's what makes short hikes the most dangerous. No matter how well they know the trail, many people never consider that they might end up unexpectedly spending the night outdoors or waiting for medical help --and so they hike without the essentials. Felix! the Sugar Glider Be Safe Hike Smart (Amazon) teaches essential day-hiking skills, items to pack, how to navigate your way with and without a map or compass, and how to get rescued. Learn to stay found by using a compass and paying attention to your surroundings. A compass doesn't need batteries and works in all types of weather but you need to know how to use it and this book makes learning --easy. This book is for all ages --parents, friends, and children can learn together. It's a fast, easy read that could save your life and will definitely make your hike more safe and enjoyable!
In taking a bearing steps 1 and 2, what is meant by boxed?
In my opinion, a beginner learning map reading skills should take a fix about every 20 minutes. Preparing the map makes this a lot easier. Use the scale of miles and make a mark on the map every 1/10th of a mile. Before looking for terrain features, estimate your position using timing and estimated speed from the last position.
For declination I use the saying "In the West, truth is greater than magnetism" The center is around Chicago or where the variation is zero on the map if close to the center of the country.
For beginning map reading, it's important to understand that the mile grid on the map measures only a flat horizontal distance. Hiking across that mile grid in hilly terrain will add distance (vertically). If the angle is 45 degrees up or down across the mile grid, that can add about 43% to the distance, making that one mile about 1.43 miles. Add curves to the trail and the distance is longer. Not a big deal if you understand this, but a stress point if you or others expect your arrival at a certain time.
ADD for East and Subtract for West??!?!?!? Hmmmmmmm . . . . I thought it was the opposite?
Read Felix! the Sugar Glider Be Safe Hike Smart (Amazon). Learn essential day-hiking skills and how to navigate your way with and without a map or compass. A fast, easy read that could save your life and will definitely make your hike more safe and enjoyable!
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