UTM, Universal Transverse Mercator, divides the world into sixty zones, each zone is six degrees of latitude and has its own central meridian.  The zones are limited at 84 degrees north and 80 degrees south.  UTM is used in the United States for topographic quadrangles at 1:100,000 scale.  Mainland United States commonly uses the Clarke 1866 spheroid with UTM.  Most of the State of Colorado is in UTM Zone 13.  To maintain a uniform projection for the whole state of Colorado, the herpetofaunal points on the Colorado Herpetofaunal Atlas Distribution Map are shown in UTM NAD83 Zone 13 Meters.