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In darkness, fog, or dense vegetation, traditional line-of-sight routefinding won’t work. “Low visibility is the worst-case navigation scenario,” says Stephen Hinch, author of Outdoor Navigation with GPS. “Even with a GPS, you won’t find your way safely if you’re glued to the screen–and not paying attention to your surroundings.” His suggestion: Always bring a map, and use these three effective strategies.
Strategy 1: Navigate with preloaded maps, tracks, and waypoints.
“Your GPS is only as good as what you’ve programmed into it,” says Hinch. Just having start and finish waypoints, which might suffice in good conditions, may not be enough in low visibility. At night or in a whiteout, you’ll want more location information.
How: Before a trip, program intermediate waypoints to guide you through safe zones, mark hazards like cliffs or steeps, and show locations of bailouts or shelters that might be helpful in an emergency. With a map in hand–even if you forgot to preload your GPS with relevant data–you can input UTM coordinates if on-trail conditions deteriorate. (Easy option: Outside+ members get premium access to Gaia GPS.)
Strategy 2: Follow short sight lines along your bearing.
When visibility is good, you’d use a compass (or your GPS unit’s compass screen) to identify landmarks near your destination, which may be many miles away. In low visibility you can do the same thing, but with shorter distances. “This technique helps you stay attuned to your surroundings, and makes you less likely to follow your GPS screen blindly into a dangerous situation,” says Hinch.
How: Take short “sight lines” to align close-in, visible features with your desired bearing. Hike between the features and when you reach the more distant target, use your compass to identify another landmark along the bearing. Continue leapfrogging benchmarks toward your destination.
Strategy 3: Travel along a steady elevation.
You can still use landscape contours to guide travel when peaks, valleys, or navigation handrails–easy-to-follow landscape features like ridges or treeline–aren’t visible.
How Identify a safe travel zone based on an elevation range and use your GPS or altimeter to stay within that range as you hike. Be aware that uncalibrated altimeters may have a 100-foot margin of error. Improve your unit’s accuracy by 50 percent or more by calibrating it every time you turn it on.