1. City-Data.com. 2008. “Sioux Falls, South Dakota”. http://www.city-data.com/city/Sioux-Falls-South-Dakota.html(accessed July 21, 2009)
2. EROS Data Center. “National satellite land remote sensing data archive”. http://edc.usgs.gov/archive/nslrsda/overview.html(accessed July 21, 2009)
3. Johnson, K. 2007. “Stanford Digital Repository”. http://library.stanford.edu/depts/dlss/collections/sdr.htm(accessed July 21, 2009)