GPS: Cutting Through the Coordinate Confusion


Several times I have offhandedly suggested that my readers simply pop the provided GPS coordinates into their phones and zip on over to the trailhead. It occurred to me that not everyone routinely uses GPS coordinates to locate … well, anything. This is a shame because GPS coordinates can be used to find trails, mark water sources, locate geographic features, or even to find where you parked your car. If you want to put these obscure-looking strings of numbers to good use, you need to understand how they designate global locations. This is not hard, but there’s a lot of confusing information out there. Let’s start with the basics.

There are two widely-used systems: the DMS system (Degrees, minutes, and seconds) and the DD system (decimal degrees). Admittedly, I really didn’t understand the differences between these  prior to to doing a lot of research. The digital decimal system will work in virtually any navigation app (like on your phone), while the degrees, minutes, and seconds format is less suited to everyday use.


The Royal Observatory in Greenwich England

Most of us have a general understanding of latitude and longitude, which are the basis for both the DMS and the DD systems of global positioning. The earth is divided north/south by lines of latitude and east/west by longitude. Each line represents one degree, just like the degrees on a protractor. You’re probably familiar with some of the major lines of demarcation – like the equator. The equator is the zero point for latitude, and the degrees are counted away from it to ninety degrees north or south – at each pole. The zero point for longitude is the prime meridian, originating at the Royal Observatory in Greenwich, England. This is also the starting point for the world’s time zones. The prime meridian (at 0°) and the International Date Line, aka the anti-meridian, (at 180°) divide the globe into eastern and western hemispheres in the same way the equator divides the northern and southern halves of the earth.

MercNormSph_enhancedUsing the DMS (degrees, minutes, and seconds) system, each degree of latitude or longitude is divided into sixty parts (minutes), and each minute is further divided into sixty seconds. By assigning a number of degrees, minutes, and seconds either north or south of the equator, and then east or west of the prime meridian, one can accurately pinpoint a specific spot on the globe. These coordinates look like this:

36° 59′ 56.7024″N, 109° 2′ 42.8022″W
Thirty-six degrees fifty-nine minutes fifty-six seconds north, one hundred nine degrees two minutes forty-two seconds west.
(the numbers after the decimal point in the seconds place are fractions of seconds for accuracy)

These are the coordinates to Four Corners, the intersection of Utah, Colorado, New Mexico, and Arizona. The first figure is always latitude and the “N” denotes north, so Four Corners is north of the equator. The “W” in the second, or longitudinal, figure tells us that Four Corners is west of the Prime Meridian. So, how do you measure these degrees, minutes and seconds? Well, you can get out a map and ruler, take measurements and use a complicated formula or … just use Google Maps. The same goes for converting from one system to the other. Google Maps is your friend.


Lines of latitude and longitude

The other format for GPS coordinates is the DD, or digital decimal system. The DD format is better suited to cross-platform use, so it works on your computer, your phone, or your GPS device. It’s cleaner and doesn’t require the use of symbols that aren’t readily available on all devices. This system works in essentially the same way as the DMS system, except each degree is broken into ten parts instead of sixty. Each of those parts is divided into ten and so on – up to at least eight decimal places. Google Maps uses six decimal places. The DD system replaces compass headings with a minus sign (negative) to denote south or west. North and east are positive numbers. Using the DD system (to six decimal places), the coordinates for Four Corners would be as follows:

36.999084, -109.045223

Four CornersThe first figure, latitude, is positive, indicating the northern hemisphere. The longitude is negative, so that coordinate is west of the Prime Meridian. Conversely, a negative latitude will be in the southern hemisphere and a positive longitude is found east of Greenwich, England. A six-decimal-place coordinate is accurate to within about 111 millimeters, or a little over four inches, so it can be used to pinpoint a rock on the trail if you so desire.

That’s the long(itude) and short of how GPS works, but how can it be put to practical use on the trail?

Hiking Upward coordinates

The most frequent way in which I use GPS coordinates is to locate a trailhead. Many websites provide these coordinates to help identify trails and/or their associated parking areas. A great example comes from a really wonderful hiking website in the mid-Atlantic region called Hiking Upward. Notice the circled coordinates in the screenshot above. Hiking Upward uses five decimal places; with an accuracy of plus or minus three and a half feet, that’s more than enough accuracy to find a parking lot – or a trailhead.

Screen Shot 2020-04-26 at 5.31.00 PMAt the end of each of my posts, I provide some logistical information: date, location, trailhead, distance, elevation gain, and my rating for the difficulty of the hike. “Location” and “trailhead” may seem redundant. It is, but I use location to identify the town or municipality (or park) in which the trail system resides. The trailhead is the exact location of my start point. Those coordinates can be copied directly from my post and dropped into the search bar on a map program. For example, these coordinates are from my Maroon Bells (read here) backpacking trip with my wife:

39.098592, -106.940648

Entering these figures into Google Maps results in the following:

Maroon Bells Trailhead

The trailhead is pinned in red. In the lefthand panel the coordinates are shown in both DMS and DD format – Google Maps easily converts one to the other.

I feel comfortable saying that most major map programs will accept GPS coordinates, although I admittedly did not test every one. Google Maps, Bing Maps, and Gaia GPS (I reviewed Gaia here) all accept digital decimal input. I also tested them as a destination on both Rand McNally online and MapQuest. In each case, I received directions taking me directly to the trailhead.

Rand McNally

Driving directions to the Maroon Bells trailhead from Aspen

Here’s another trailhead – try copying this into Google Maps:

63.990759, -19.062852

You should have been transported to a spot just west of the Landmannalaugar Tourist Information Center in Iceland’s southern interior. This was the trailhead for another four-day backpack down the Laugavegur Trail to Þórsmörk (read here).

Rhyolite in the mountains

Headed down the Laugavegur Trail

An even more practical use of these global positioning coordinates is to enter them directly into your phone or other navigation device. I use the navigation app “Waze” on my iPhone. All I need to do is enter the coordinates into Waze, click “Go Now”, and follow the turn-by-turn directions to wherever I have decided to hike that day. Of course it’s important to enter the information accurately if you can’t copy and paste. The most frequent mistakes I make are to forget the comma after the latitude or to omit the space between the two figures.

IMG_6373What if you’ve found a hike on the map and want to get coordinates for the trailhead? Using Google Maps, simply place your pointer over the trailhead and click. A small grey pin will appear where you clicked, and at the bottom of the screen a pop-up will appear with information. In this case Google knew I was at the Lost Mine Trail (read here), but sometimes only a municipality will appear. The pop-up also shows that the location is in Big Bend National Park, TX, gives the zip code and, lastly, the GPS coordinates to six decimal places. I can now copy and paste that value into my navigation app.

Lost Mine Trailhead

The small grey pin is circled in red

Lost Mine 2

The pop-up

There are a myriad of uses for this technology. Find a spot along a trail with a spectacular view and want to share it with a fellow hiker? Drop a pin with an app like Gaia GPS and share the coordinates. Your friends can use them as a guide directly to the view you wanted to share. Discover a reliable water source on a rim-to-rim hike in the Grand Canyon? Yeah, yeah, I know that’s really far-fetched. If you did though, you’d want to share that with the park service and anyone you might benefit from that potentially live-saving information. Save the coordinates. Mark the location where you stashed a food drop on a long thru-hike. In the Bisti/De-Na-Zin Wilderness (read here), where there were no trails, Lisa used pre-pinned GPS coordinates to navigate to specific formations she wanted to see. You could even use this to help a friend find you in a crowded football stadium. I mean, not right now of course, but hopefully someday soon!


Lisa pinned locations and then navigated to them in the trail-less Bisti Badlands

Rowley's Bay Pin

The green pin on my Rowleys Bay hike (read here) marks a bench with a beautiful view over the bay – a perfect spot for a break!

Understanding and using GPS coordinates are a great way to navigate in the backcountry. They are vastly more accurate than a street address and work anywhere on (and off) the trail. In another country and don’t speak the language? Every country speaks GPS. So if I ever post about a hike that you want to take, simply pop those GPS coordinates into your phone and zip on over to the trailhead!  ♦

5 thoughts on “GPS: Cutting Through the Coordinate Confusion

  1. This is very helpful; thanks for the post. A question: in your coordinates shown above (39.098592, 106940648), should there be a period after the 106 or somewhere in this second string of numbers?

    Liked by 1 person

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