Map compiled by merging and PhotoShop editing layers from the National Atlas including:

• United States Average Annual Precipitation, 1961-1990: http://nationalatlas.gov/mld/prism0p.html [map layer compiled from Oregon State University-PRISM Climate Mapping Project data]
• Cities and Towns of the United States: http://nationalatlas.gov/mld/citiesx.html [map layer compiled from the USGS Geographic Names Information System (GNIS) and U.S. Census Bureau data]
  
• Major Roads of the United States: http://nationalatlas.gov/mld/roadtrl.html [Map layer compiled from unspecified resources by the USGS in colaboration with the Federal Highway Administration (FHWA) and the U.S. Department of Transportation]