How Do GPS Coordinates Work?

So, you’ve probably seen geographic coordinates like these before, maybe on a GPS device, or maybe scrawled in a mysterious note you found in the glove box of a rental car

So, you’ve probably seen geographic coordinates like these before, maybe on a GPS device, or maybe scrawled in a mysterious note you found in the glove box of a rental car. But if you never knew exactly what they meant, fear not – it’s pretty simple, and we are here to make it all clear. *Intro music* When you see a set of geographic coordinates looking like this or like this, you’re reading

latitude and longitude. Latitude represents north-south location, and longitude represents east-west location, usually listed in that order. By combining them, you can pinpoint any spot on the surface of the earth. These coordinates aren’t expressed in units of distance but in degrees. Why?

Because the earth is a sphere. Imagine a line running from the equator to the centre of the earth, and then another line running from the center of the earth to the north or south pole. These two lines make a 90-degree angle. All latitudes in each hemisphere can be represented by drawing a third line somewhere between them.

So the equator would have 0 degrees latitude, and the north pole would have 90 degrees north latitude, and a location halfway between the north pole and the equator would lie at 45 degrees north. Same thing for the southern hemisphere, except you’d call it degrees south. For more precision, each degree of the earth’s surface is divided evenly into 60 “minutes,” and each minute is divided into 60 “seconds.”

If you need to get even more specific, you can just add decimals to your seconds. Alternately, you can write the whole coordinate in decimal notation. To do this, you have to convert minutes and seconds, which are base-60, into our regular base-10 counting system by dividing each unit by sixty and then summing them up. The results sometimes look counterintuitive, but if you’re skeptical you can pause the video and check out the math.

Lines of longitude, also called meridians, run north-south and are used to measure position along the east-west axis. While the lines of latitude run parallel to each other, meridians converge at the poles and spread farthest apart at the equator, like the segments of an orange. Longitude is also measured in degrees, but its zero-degree line is known as the Prime Meridian, and it runs from the North Pole to the South Pole through Greenwich, England.

So if the Prime Meridian is zero degrees, the opposite side of the earth is 180 degrees, and lines in between are expressed as degrees east or degrees west, between 0 and 180. Since the lines of latitude are parallel, each degree covers about the same distance the world over – roughly 111 kilometres. But because meridians converge at the poles, the distance covered in each degree of longitude varies hugely depending on your latitude.

At 20 degrees North, which is about the latitude of Cuba and Hawaii, one degree of longitude is approximately 104 kilometres. At 80 degrees North, the latitude of Svalbard and northern Greenland, it’s only about 19 kilometres. So let’s say I wanted to go dig up a stash of hot loot from some coordinates I found written in a mysterious note.

Even without looking at a map, we can start to make a guess where this would be. Since it’s 43 degrees north, it’s almost halfway between the equator and the north pole -- again, halfway being 45 degrees. And since it’s 89 degrees west, it’s almost halfway west between the prime meridian and the opposite side of the globe -- halfway being half of 180 degrees, or 90 degrees. Based on this alone, you can guess it’s probably somewhere in North America.

But if we use a map or a digital tool like Google Earth, we can zoom in and see these coordinates lead us to ... the U.S. National Mustard Museum in Middleton, Wisconsin. Huh. What’s the weirdest landmark you’ve ever found on Google Earth? Paste the coordinates in the comments so everybody can check it out. If you liked this video, hit that thumbs-up button, and subscribe for more.

And as always, for answers to all kinds of questions like this, head over to HowStuffWorks.com.