Over the past few years, phone GPS has gone from basic directions to full-blown maps on smartphones that show the user’s exact location. While Google Maps is the preferred program for driving, the map portion requires a cell signal to properly work, which negates its usefulness in backcountry where reception can be spotty. There are, however, numerous apps for smartphones that allow users to download topographic maps. Prices range from $.99 to about $10 for both Android and iPhone versions that allow smartphones to be turned into a full-blown, handheld GPS unit. However, phone GPS have the same issues as handheld units; small screen size, limited battery life and potential for getting lost or damaged. Users should still carry a map and compass.
Another issue with GPS units is Datum. A lot of USGS topographical maps are based on the NAD27 (North American Datum of 1924) Datum. However, most GPS units default to the WGS84 (World Geodetic System of 1984) Datum. These two systems have a difference of about 630 feet, or a tenth of a mile. Of course, some areas have been updated, while others haven’t. It’s important to know how to read a map legend, and how to change a GPS unit to match the map’s Datum.
By J. Martin
It wasn’t that long ago when the idea of an electronic device determining a person’s location down to a few yards was something out of a science fiction novel like Robert Heinlein’s Starship Troopers. Today, however, global positioning satellite (GPS) is just a part of life.
Over the past few decades, GPS units have moved from military-only hardware to being carried by the “gadget guys” to pretty much universal use. GPS units are now used by many folks to make navigation easier by guiding them to everything from a popular deli for a pastrami sandwich, to a friend’s house across the country and everything in between. There are numerous brands of portable units designed for vehicles, and few people head into the backcountry to hunt, fish or hike without a handheld GPS unit to guide their way. After September 11, Federal guidelines require that even cell phones activate a GPS chip when used to dial 911, and most of today’s smartphones have GPS and mapping software to make traveling ultra-convenient.
The problem with this convenience is that people have become reliant on it and are quickly losing the ability to navigate. It’s as if GPS has replaced conventional maps in many people’s minds, even though the system was designed as a compliment, not a substitute.
“The utility of GPS receivers cannot be understated,” said Jonathan Horne with Rocky Mountain Rescue in Boulder, Colo. “But relying on them as a sole navigational tool, especially in the backcountry, is dangerous.”
GPS handheld units use either latitude/longitude lines or the Universal Transverse Mercator (UTM) grid coordinate system to show where the user is located pretty much anywhere on Earth. Longitude/latitude lines are listed on maps in degrees, minutes and seconds, while UTM grids are listed as a block number. Some maps list both longitude/latitude and UTM, while others only list one. Most GPS units can be programmed to either system, so users can swap to their preferred system or whichever system is listed on the map. Of course, to properly use a map and GPS together, one must understand how to read a map to obtain a location and plan a route.
“GPS is no replacement for map and compass,” said Jeff Caulfield, Magellan Outdoor Products Trainer. “GPS navigates as the crow flies. Maps show lakes, mountains and other terrain features, and allow you to plan a safe, passable route. Maps allow you to see larger areas in just as good of detail. You can see the bigger picture and plan accordingly.”
One benefit of GPS devices is magnetic declination. The difference between true north and magnetic north can be off by several degrees, depending on location. Maps are written on true north and provide the basic declination for the area that it lists so it can be adjusted for on a compass. With GPS units this is not a factor as the electronic compass can be programmed for either true north or magnetic north modes, depending on need.
By understanding how to read a map and compass, travelers can use a GPS units sparingly and save battery power for when the unit is truly needed, such as when hopelessly lost. Learning to combine the two is simple; the hard part is learning to properly use a map and compass. However, that only takes practice, which can be obtained by trekking into the woods.
Simply start at a trailhead and follow your progress on a map by marking landmarks that you can see. Once you have traveled a significant distance, determine your location on your map and use the GPS unit to discover your accuracy. If you’re not correct, sit down and figure out why, and try again. Mentally retrace your route and visualize the landmarks you passed.
“There’s no substitute for experience,” said Horne. “Bunched-up contour lines take on a real significance when you’re standing atop a cliff edge. Bring a map and compass. Bring a GPS. Learn how they work and how they work together.”
To determine a route on a map and GPS unit together, first obtain your current location on the GPS. From there, orient the map to true north and mark your current location on the map. Then find the desired travel point on the map and figure the location’s coordinates on the map and plot the general direction and measure the distance. Map scales range in size, USGS topographical maps are most often listed in 1:24,000 scale. This means 1 inch on the map equals to 24,000 inches, 1 centimeter equals 24,000 centimeters and 1 foot equals 24,000 feet on the ground. All this equals .378 miles. Usually, there is a distance scale in the key showing mile and half-mile increments.
Once distance has been determined, look at the contour lines to determine the best route, remembering that the closer the lines, the more steep the terrain. The preferred route can be loaded into a GPS unit, with multiple waypoints along the route to ensure that the user doesn’t get off path.
Of course, some GPS units also allow maps to be downloaded and viewed on the unit in conjunction with points of interests and the user’s location. This can be very useful for tracking distance traveled, speed and estimated time of arrival. Later that information can be uploaded to a computer to share with friends or to create custom maps.
However, the screens on most GPS units are three to four inches at most, meaning users must choose between viewing up close detail and the overall picture by zooming in or out on the unit. Maps have the ability to show both extreme detail as well as the overall picture. And while maps and compasses can become damaged or lost—just like GPS units—they don’t run out of battery power.
