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2. Staffing, capacity, and ambulance diversion in Emergency Departments: United States, 2003–04;Burt;Adv Data,2006
3. GIS.com: the guide to geographic information systems. What is GIS? Available at: http://www.gis.com/whatisgis/index.html Accessed December 5, 2008.
4. Principles of geographic information systems;Burrough,1998
5. Census 2000,2001