Monday, December 20, 2010

Finding your way -- GPS for genealogists

http://www.navcen.uscg.gov/ftp/gps/ggeninfo/gps-iif.tif
My early experiences mountain climbing and exploring caves helped me develop a pretty strong sense of direction. I seldom get lost, especially in the Western U.S. But after a few experiences in the Eastern States, I can surely appreciate maps and directions. One time driving in Pennsylvania we were trying to find our way to Harrisburg from Philadelphia and managed to end up in Wilmington, Delaware. Fortunately, that is the only time I can remember ending up in the wrong state. Since I spend most of my life in Arizona and Utah, I hardly ever consult a map, unless we are trying dirt roads. As a result, I have never felt I could justify having a GPS (acronym for Global Positioning System).

Surprise, I got a GPS with my iPhone and guess what? It is useful for things other than keeping from getting lost. I have found uses for the devices that I never would have imagined. GPS is sort of like Arthur C. Clarke's Third Law, "Any sufficiently advanced technology is indistinguishable from magic." It is magical to run an App on my iPhone that shows exactly where I am with a blinking blue dot, even if I can look out the window or open my eyes and I know exactly where I am. What I find is that I don't know where everything else is.

So let's say I want to get to the National Archives in Philadelphia (back to Pennsylvania, my best example of someplace where you really need directions to get anywhere). With any of dozens of models of GPS devices, I can use either an online database (like with my iPhone) or a pre-installed one to locate the building and then simply push a button for directions from where ever I happen to be at the time. On some models, a friendly voice will even tell me when to turn right or left or whatever to get to my destination. We find that we also use the iPhone's GPS to locate stores, restaurants, and just about every other kind of business we need. I recently used the iPhone with Google Maps to find the Riverton Family Search Library in Riverton, Utah. By the way, the location and address are not obvious or very easy to find from the street. The building is off the main street behind a large shopping center. But with Google Maps satellite view, I could actually see the building. I was never lost but the building was not easy to find and I was glad I had a live GPS map to work with.

It might be a good idea to give a short summary on how GPS works. Most people now use the term "GPS" to refer to any number of small electronic devices that use either the Global Positioning System of 27 Earth-orbiting satellites (24 in operation with 3 extras for backup) and/or cell phone towers, to determine the device's approximate location. The device receives the signals and once it has four or more signals, it uses the the time it takes a signal to travel from the satellite to the receiver and then computes the distance to each satellite. The receiver then uses a method of trilateration, that is calculating the intersections of three spheres, to determine the location of the device. Trilateration methods involve the determination of absolute or relative locations of points by measurement of distances, using the geometry of spheres or triangles, In contrast to triangulation it does not involve the measurement of angles. (It is sounding more and more like magic all the time).

The last time I checked, the Earth was an oblate spheroid, so any location on the surface of the Earth can be represented by the intersection of two lines. These lines are usually referred to as latitude and longitude. There is an arbitrary zero point for both and any point on the Earth's surface can be represented by its coordinates. For example the National Archives in Washington, D.C. is located at

38° 53′ 34.01″ N, 77° 1′ 22.71″ W
This is an almost exact location on the Earth. No other place has these same coordinates. Just for information sake, there are actually two systems of GPS, one very accurate one used by the military and another one that is more or less accurate used by everyone else.

OK, so let's suppose you want to find a cemetery in Pennsylvania. For example, the Westminster Cemetery. Finding someplace like this is now almost trivial. All you do is enter in name of the cemetery into a search engine, such as Google, and you almost instantly have an address with a link to Google Maps to show you exactly where it is located. If you are driving and enter the address into a GPS device it will calculate the distance and give you directions.

Let's make the problem a little more difficult. Let's say you are trying to find Latuda, Utah. Doing a Google search produces a map with no details at all, not even the name of the place. It is on a road called Spring Canyon, so how do you know when you get there? You don't. This place turns out to be an abandoned mining town (i.e. ghost town). There is only one building left standing and without some specific map directions you would never find it. But, if you have the coordinates, you can drive right to the location with a GPS receiver.  Well, let's say this, you can drive right to the location assuming you have the usual mandatory Utah/Arizona high clearance vehicle. If you are interested, Latuda is about five miles west of Helper, Utah. Oh, you say, that explains it exactly.

One of the most important things to remember when using a GPS receiver is when to ignore it. My daughter routinely uses one to drive around in Texas. One day taking my grandson to summer school I used the GPS and ended up in a cul-de-sac about two miles from the school. They are not infallible. For some reason in that part of Texas, the locations are sometimes off by as much as a mile or more.

Some of the newer software programs have the ability to geocode locations. This means they will look up the location in a database and add in the coordinates if the place is found. Good news. Bad news. The good news is that having the coordinates is very useful in finding the places on a map. The bad news is too often the places you are looking for no longer exist on modern maps. But, if you have the coordinates, it doesn't matter if the location is still on a map or not you can use a fancy GPS receiver to drive, walk, boat or whatever to the location. Let's see, I could always do that with a topographical map and the map didn't need batteries. So why do I need a GPS? Convenience? Not having to try and find the right topo map every time I want to find something? There are reasons.

Other than the cell phone version in my iPhone, there are two major types of GPS receivers, those made for hikers and those made for drivers. Before you buy one or the other, you may wish to analyze how and where you might use the device. If you plan on hiking out into the wilderness, a car based receiver is almost useless. On the other hand, if you plan to use your device for finding houses and places of business, you may get along perfectly well with a vehicle based system.

What about cost? Just a short time ago, even the most rudimentary GPS receiver was extremely expensive. Like most electronic devices time has eroded the price to point of ridiculousness many very full featured models are less than $100. They now come in color, with maps, and lot of  other bells and whistles. However, like most electronics, if the price seems too low to be real, it is probably an outdated, last on the shelf, item.

2 comments:

  1. I used it to record the positions of family gravestones in cemeteries that my daughters have not visited--not yet anyhow. (C'mon, girls. Look how easy I made it for you!)

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  2. Don't feel bad about getting lost in Philadelphia, you could have also gone to New Jersey or Maryland.

    Philadelphia is a tricky city to drive in, I worked there for two and a half years and rode the train into the city.

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