United States National Grid

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The United States National Grid, officially known as the United States National Grid for Spatial Addressing (USNG), is a system of geographic grid references commonly used in United States, different from using latitude or longitude. It is similar in design to the national grid reference systems used throughout other nations. The USNG was developed by the United States Department of Homeland Security (DHS), and is administered by the Federal Geographic Data Committee.

[edit] Overview

The purpose of the USNG, as defined by the DHS, is to "create a more interoperable environment for developing location-based services within the United States and to increase the interoperability of location services appliances with printed map products by establishing a nationally consistent grid reference system as the preferred grid for NSDI applications. The U.S. National Grid is based on universally-defined coordinate and grid systems and can, therefore, be easily extended for use world-wide as a universal grid reference system." [1]

It is based on the Universal Transverse Mercator (UTM)[2] system used by the US Military. By setting your GPS to display coordinates in UTM and to use the standard WGS_84 Datum that most GPS units default to, your position in the USNG is automatically displayed.

In addition, it has the advantage of being easily plotted on USGS topographic maps by using a simple "left to right and then up" method instead of having to plot "backwards" from right to left when using latitude and longitude in the Western Hemisphere. The coordinates are also easily translated to distance as they are actually in meters. Thus the distance between two coordinates can quickly be determined in the field.

You can download USNG 1 sq.km Grid state-wide polygons for select states at http://mississippi.deltastate.edu. You will also find more detailed information about the US National Grid.