The study found that geographically, cases of assault with a firearm were concentrated in a few areas of the city, and self inflicted incidents were relatively diffuse across Philadelphia compared to the general population. Firearm violence was said to be the end result of a causative web of individual-level and geographic risk factors. Few, if any, studies of firearm violence have been previously able to simultaneously determine the population-based relative risks that individuals experience as a result of what they were doing at a specific point in time and where they were, geographically, at a specific point in time. New methods and applications of these linked data relevant to researchers and policymakers interested in firearm violence are also discussed. This paper describes the linkage of individual and geographic data that was undertaken as part of a population-based case-control study of firearm violence in Philadelphia, PA from October 2003 to April 2006. The study used telephone interviews and existing data sources to include police reports; medical examiner and hospital data; population, demographic, and geographic data; and firearms dealer information from the Bureau of Alcohol, Tobacco, Firearms and Explosives. Figures, tables, and references