How Does GPS Work?

How Does GPS Work?

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By Natalie Josef July 19th 2012


A couple of months ago, I was riding in a friend’s car as we drove across the Bay Bridge from San Francisco to Oakland. She had a navigation system that was pretty neat and had already helped us navigate around some road construction and one-way streets. Though I didn’t like the tone of the lady bossing us around, I had to admit the navigation system was pretty cool.

When we were in the middle of the bridge, suddenly, the little arrow that was us moved off the roadway and into the San Francisco Bay. This, of course, prompted me to laugh my butt off because all I could think about was what that cranky lady would say if we were really in the water—float .6 miles and turn left at coral reef. Or what she would have said if we had been super literal and actually followed the little arrow to a watery grave. Recalculating route …

GPS Gone Wrong

We have heard tons of stories of GPS systems gone wrong—people driving onto train tracks, nearly over cliffs, the wrong way down a one-way street. Some folks have even sued for damages after Google Driving Directions deposited them into a rice field or a shooting range instead of the Walmart parking lot. I won’t go into the psychological reasons why people will follow GPS directions to the bitter end, despite all other indicators that they are headed for a swamp. Obviously, some people could use a little common sense, but if you are lost or in a new area, you need to trust the GPS lady—you don’t have a choice. 

For all the GPS stories gone wrong, there are obviously many more stories of GPS systems successfully helping you navigate to your destination. But those stories aren’t very interesting and don’t make it to the news. Still, all of this just makes me wonder—how did these systems get the directions in the first place?

How GPS Systems Get Their Driving Directions

I always thought that these systems get their directions from a guy driving in his Ford Taurus littered with fast food wrappers and convenience store coffee cups. I pictured him with a spiral notebook and blunt pencil, documenting every curve in every road in Bell Buckle, Tennessee before retiring to his room at Motel 6.

Turns out, I am not that far from the truth.

Before all the algorithms, computer software, and satellite imaging, you need hard data that comes only from field work. Whether you are punching in driving directions into your car’s GPS system or trying to find the nearest Pakistani restaurant on your iPhone, companies like NAVTEQ are at the core. They employ geographic analysts who go into every city, big and small, and actually drive the roads and record the data.

To get an authentic driving experience, the analysts drive the roads at various times of the day, i.e., during peak traffic times or in the middle of the night. They record all pertinent data—everything from forks in the road, dead ends, and bodies of water, to park land, the quality of road surfaces, and telephone poles. Since roads are always changing, this is an ongoing process and always will be.

How Global Positioning Works

We could go into the atomic clocks and 3D trilateration mumbo jumbo, but let’s not. For the sake of brevity, basically, after the street level data is collected and uploaded into computer software programs, the data is plugged into the Global Positioning System (GPS), which consists of twenty-seven satellites that orbit the earth two times a day. Twenty-four satellites are always in operation, while three exist as backups. The orbits are organized so that at least four satellites are visible from any location on Earth at any time. 

Your car’s GPS receiver “locates” at least four of these satellites and uses triangulation to pinpoint your exact location. As you drive around, the signal is repeatedly updated so your receiver can tell you where to go. The more accurate the initial data collection was, the more accurate your driving directions will be. 

The Bottom Line

There are a whole bunch of smarty-pants who have worked for years, and will continue to work for years, so you and I can get from Point A to Point B as safely and quickly as possible. Let’s appreciate and honor this amazing technological miracle by using a little common sense. If your unit tells you to turn down a one-way street or drive off onto a gravel road in Death Valley, use a little self-control. Since GPS systems need to “see” satellites in order to work, you aren’t going to get much help if you end up in the bottom of a lake. There is only so much “recalculating” the GPS lady can do.

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