How to Convert Latitude to a Grid Reference

Written by ryan cole
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How to Convert Latitude to a Grid Reference
A globe showing whole degrees of latitude and longitude (Globe and Hand image by Towards Ithaca from Fotolia.com)

Latitude and longitude are often written in a form with degrees, minutes, seconds, sometimes fractions of seconds and a direction letter for north, south, east or west--for example 38 degrees, 53 minutes, 42.4 seconds N latitude and 77 degrees, 2 minutes, 12 seconds W longitude for the location of Washington, D.C. Designations like those are in radians, but you can convert them into decimal degrees, which then work well as a reference on a Cartesian coordinate-style grid--the kind used when working with graph paper in math classes. By convention when using decimal degrees, 0 latitude is the equator and 0 longitude goes through Greenwich, England. Everything south of the equator is negative latitude, and west of Greenwich to the International Date Line is negative longitude.

Skill level:
Moderately Easy

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Instructions

  1. 1

    Divide any seconds in your latitude by 60. This will convert it from radians to decimals. Your result should be between 0 and 1. Using the latitude of Washington as an example, 42.4 divided by 60 gives you 0.7067.

  2. 2

    Add the result to minutes. For example, 53 + 0.7067 = 53.7067 minutes.

  3. 3

    Divide by 60 again. Again, the result should be between 0 and 1. For example, 53.7067 / 60 = 0.895.

  4. 4

    Add the result to the degree. Continuing the example, 38 + 0.895 = 38.895 degrees. If latitude is N (north) or longitude is E (east), this is your grid reference.

  5. 5

    Put a negative sign on it if the direction was S (south) for latitude, or W (west) for longitude. Using Lima, Peru as an example, which is at 12 degrees, 2 minutes, 36 seconds S and 77 degrees, 1 minute, 42 seconds W, the converted latitude would be -12.043 and the converted longitude would be -77.028.

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