Map Datums and Decimal Degrees

Map Datum: A map datum is a mathematical way to describe the earth with constant reference points. There have been many mathematical models developed as the ability to measure the earth improved. The Department of Defense has standardized on the World Geodetic System 1984 (WGS 84) while the U.S. Federal Government has adopted North American Datum of 1983 (NAD 83).

The following links provide a more detailed discussion of map datums:

Most GPS units use WGS 84 as the default setting. You should not have to reset the map datum on your GPS unit to use the aerial maps of school trust lands but you may want to check your setting to be sure that it is set to WGS 84.

Decimal Degrees: The way that most of us learned latitude and longitude in school was using degrees, minutes and seconds. This is not the most efficient or accurate way to display coordinates. For these reasons, section corner coordinates on maps of school trust lands are displayed in decimal degrees. For example; 46 degrees, 30 minutes would be 46.5 degrees (dd). There is no need to convert between the two systems, simply use addition and subtraction to work with decimal degrees.

Most GPS units default to degrees, minutes and seconds. You will need to set your GPS to use decimal degrees (dd) when using it with maps of school trust lands.


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