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Decimal Degrees vs. Degrees, Minutes, Seconds

By Len Morse

Close-up of a milestone
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Updated May 27, 2014
When you hear about metric measurements, usually you are bombarded with terms denoting length, height or volume, depending on your industry. Outside of formal schooling, you almost never hear about the geographical side of measurement - specifically, those ever-present invisible lines of latitude and longitude. This article will explore how some metrics are shown in geographical terms, who uses traditional Degrees/Minutes/Seconds, and what the future may hold.

A Brief History of U.S. Metrics

Originating in France in the 1790s, the metric system (officially known as "SI", short for "Le Systeme International d'Unites") grew in popularity due to increasing global commerce. Through trade with Europe, the U.S. awareness of metrics trickled into existence, eventually prompting Congress to permit its use in 1866. It was legal, but voluntary.

The first official legislation concerning metric conversion was passed by Congress in 1974, adding metrics to our elementary and secondary education curriculum.

One year later (in 1975), Congress passed the Metric Conversion Act, declaring that the U.S. federal government should use metrics as its preferred measurement system, as evidenced by a box sitting in my cubicle whose labeling instructions tell of letters that must be "3.81cm (1.5 inches)" high. The nutritional information on any package of food is also a good example, showing grams (instead of ounces) of fat, carbs, vitamins, etc.

Ever since its beginnings, the U.S. government has striven to promote and stabilize metrication, with limited results: mostly those in the sciences, military, engineering, manufacturing and other technical fields use the metric system.

The general public, however, continues to show comparatively overwhelming disinterest in adopting grams, litres and meters over the traditional ounces, quarts and feet. The United States is the only remaining industrialized country whose general population does not use metrics as its primary measurement system.

To see more details, dates, FAQ's and other information, visit the U.S. Metric Association (USMA) web site.

Metrics and Geography

Despite the average American layperson's apathy for metrics, those of us who use geographic coordinates on a daily basis see plenty of evidence that decimals are out in full force. On any given day I'll see a few handfuls of engineering site surveys (and sometimes other data) come across my desk, 98% of which have a decimal somewhere in the latitude or longitude.

As technology has developed over the years, allowing more accurate measurements, the number of ways that we geography people get to read those coordinates has increased. The three most popular types of Lat/Lon displays are:

  • Traditional degrees/minutes/seconds (D/M/S), usually with decimal seconds
  • Degrees with decimal minutes, no seconds
  • Decimal degrees, no minutes, no seconds

Doing the Math

No matter how you choose to display them, any converted coordinates will get you to the same point, basically - it's simply a matter of preference. If you are one of those people who grew up learning only D/M/S like me, you might break into a cold sweat the first time you see the second or third decimal variations (bulleted above), if only from the memory of your high school algebra classes.

But fear not, for there are a boatload of conversion programs and web sites that will do the math for you. A majority of these sites convert between D/M/S and decimal degrees, leaving out the less popular but still available decimal minutes. One of the few sites that convert for all three is TerraServer.com the degree conversion page.

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