In the Beginning

Latitude and Longitude

First article in a seven-part series

Being round, it was easy to point out that these two circles (like all circles) comprised 360 degrees of circumference, so if you started a journey at the exact point where the equator intersects the prime meridian near Africa and continued west, halfway around the globe, to arrive at the point where the two circles intersect again, you would have traveled 180 degrees (written as 1800).

Using the same parts of circles as measurement then, we can describe any location in North America as being so many degrees north of the equator and so many degrees west of the prime meridian. Examples:

Toronto is approximately 430 north of the equator and 790 west of the prime meridian.
Philadelphia is about 400 north of the equator and 750 west of the prime meridian.
Los Angeles lies almost 350 north of the equator and 1180 west of the prime meridian.

Other world locations are also measured by their relationships with the two main circles. For instance:

Brisbane is 270 south of the equator and 1530 east of the prime meridian.
Moscow is 560 north of the equator and 380 east of the prime meridian.

Fractions of a degree can be expressed in "minutes" (there are 60 minutes in one degree). A minute may be further divided into seconds, but, for our navigation purposes, it's easier to measure locations in degrees/minutes/decimal-minutes. Using this system, I would write the location where I live as:


meaning 46 degrees, 19-point-5 minutes north of the equator and 79 degrees, 22-point-6 minutes west of Greenwich, England, and the prime meridian.

We call that measured location a set of coordinates. In GPS lingo it would be a waypoint . . . same thing. Here's how it looks on a Garmin GPS screen.

There is no other location on the globe with the same coordinates. Change the "N" to "S" and I would be living somewhere in South America. Change the "W" to "E" and I'd have moved to somewhere in Russia.

In geographic terms, north and south coordinates are called latitude while east and west coordinates are called longitude. In short form, the system is known as lat/lon.

Here's an example of how valuable it can be to be able to measure your location from a map or with a GPS unit.

You and your friends are sharing a great hike across the backside of nowhere when one of the party suffers a severe injury. Fortunately, you're equipped with a cell phone (please don't start THAT debate again) or a radio and you're able to contact a ranger station.

The friendly ranger agrees to alert search and rescue for a helicopter to come and get the injured party and then says, "Okay, where are you?"

Without a good topographic map and navigation skills—or a map and GPS unit—you might reply, "We're on the west side of Wild Horse Canyon, maybe three miles back in the pines and there's a stream near here and a big rock pinnacle to the south." Not much for the ranger or the pilot to go on unless they really know the country.

But . . . you've got your map out and the GPS is winking lat/lon coordinates on the location screen and you say, with confidence, "We're at north 38 degrees, 17-point-2 minutes; west 105 degrees, 28-point-7 minutes."

The ranger relays the numbers to the pilot, who dials them into his on-board GPS, checks the map on his knee, and lifts off for a direct flight right to your location . . . guided all the way by a GPS steer. There's no search—only rescue.

Published: 30 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication


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