This directory contains USGS Digital Raster Graphics (DRG). These files are the created by scanning the USGS topographic maps. They are simple TIFF images and can be viewed with many standard graphic programs. Each ZIP file contains the TIFF and a 'world' file. This file is needed if you are going to bring this image into some kind of Geographic Information System (GIS). These files are projected into a Universal Transverse Mercator (UTM) Projection System. The files fall into two UTM Zone. Zone 13 and Zone 14, with the break point between the two zone occuring at -102 degress Longitude. The names correspond to the USGS Numbering scheme that uses Latitude, Longitude, row letter, and column number. For example 46099A4.zip is located within the a block defined by 46th degree north latitude and -99th degree west longitude. These images were created to be displayed at the 1:100,000 scale. Please see the file "List.txt" for a name and number relationship.