USGS – “US Topo quadrangles are digital topographic maps produced by the National Geospatial Program of the U.S. Geological Survey (USGS). Created in the familiar 7.5-minute quadrangle format like the legacy paper maps, US Topo maps support frequent updating, wide and fast public distribution, and basic, on-screen geographic analysis. US Topo maps are available for free Web download from the USGS Store. Each map is delivered in PDF format with geospatial extensions (GeoPDF®) and is made from key layers of geographic data – orthoimagery, transportation, geographic names, topographic contours, boundaries, hydrography, structures, and woodlands – found in The National Map. The National Map is a nationwide repository of integrated data from local, State, Federal, and other sources. Recent US Topo maps also include the Public Land Survey System (PLSS) and the United States National Grid (USNG). Users can turn US Topo data layers on and off as needed, zoom in and out to examine specific features or see a broader area, and print the maps in their entirety or in customized sections on a broad array of printing devices. Viewing and analytical tools are available for free download from Adobe and TerraGo Technologies. File size for each US Topo is about 15-20 megabytes. US Topo maps are produced by the USGS National Geospatial Technical Operations Center. The first US Topo prototypes, “Digital Maps – Beta,” were made in June 2009. A limited number of these maps were made spanning 18 states. As of October 2012, the prototype maps were replaced by US Topo maps and the “Digital Maps – Beta” prototype maps are no longer available. More information about US Topo maps can be found here.”