Use Your GPS, But Use Your Head

IRS-GPSGPS has got to be one of the coolest products of the Space Age. Declared fully operational less than 20 years ago, many people wonder how we ever got along without it.

GPS, originally developed for military use, was first made available to the civilian world by the Reagan Administration in 1983, following the downing of Korean Airlines flight 007 by the USSR. It was hoped that by making precision navigation available to non-military personnel, such tragedies could be reduced by cutting down the chance of accidentally straying into hostile territory. It uses a network of 24 satellites in overlapping orbits so that, at any given time and place, there should be at least 3 above the horizon. At least 3 satellites are required to give a surface position; at least 4 are required for position and altitude. The more satellites “visible,” the higher the accuracy.

You probably already know how useful modern mapping GPS receivers are for finding your way around a strange neighborhood, but GPS is used worldwide by aviators, sailors, hikers, and virtually anyone who needs to know where they are. There is even a game invented by GPS owners, called Geocaching, where someone hides a small container of trinkets, posts the coordinates, and others try to find the container using the coordinates. If you Geocache, you can truthfully say your hobby is “Using billion-dollar military satellite technology to find Tupperware hidden in the woods!”

The accuracy of consumer-grade GPS used to be only about 300 feet, deliberately degraded from the military precision level of 66 feet, until President Bill Clinton ordered the “Selective Availability” turned off as of May 1, 2000. Now, on a good day, consumer-grade accuracy within the U.S. can be as little as 10 feet, depending on how many satellites are above the horizon. A sailor once told me a story about his first GPS navigation adventure, when he didn’t have a device with built-in maps. He read the coordinates from his GPS on the bridge, then went below to plot them on his chart. When he plotted his position, he said to himself, “I knew that GPS was junk! According to this, I’m on land!” Just as he was saying that, he ran aground!

This is a good place to dispel a myth about GPS: GPS satellites can not track your location. A GPS satellite is merely a beacon transmitter, like a 21st Century lighthouse, that your receiver can translate into a position. Now, a phone equipped with GPS and the proper software can track your position, with or without your knowledge. That’s because the phone itself does have a transmitter which has nothing to do with the satellites. There are also many devices on the market that can send positions either to a website or via text messaging. These are very useful for sailors and aviators in emergencies.

The tendency to rely too much on our Electronic Enslavement Devices can be very dangerous, maybe more so with GPS than most things. Stories have been told of folks getting stranded for days or driving off of bridges because they put too much faith in the electronic map. Remember, maps always have errors because they are made on Earth by human beings, and just because the map is in a seductive black box or phone, they are no less error-prone. Google maps used to have directions from Chicago to London that included “Swim across the Atlantic Ocean…”

GPS itself, while very reliable, is not perfect. There are many ways for a position to be reported erroneously, off by feet or even miles. Rarely, there may not be enough satellites visible at a given location for a fix (This condition usually only lasts a few minutes). GPS signals can be jammed, and do not penetrate earth or walls, so positions indoors or in tunnels, etc. should not be trusted. All of this is just to say, pay attention to your surroundings. You’re not “flying on instruments” here. If you’re going to be way off the beaten path, it’s a good idea to have a backup system in case you need to navigate the old fashioned way. This means, at the very least, a paper map and an ordinary magnetic compass. The life you save may be your own.


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