A geographical analysis machine (GAM) is an exploratory method for the detection of the raised incidence of some phenomenon in an at-risk population. The name and its acronym were coined by Stan Openshaw and others in 1987. The method was developed at the Department of Geography at the University of Newcastle in the mid-1980s in an attempt to determine whether spatial clustering was evident in the incidence of various cancers in children in northern England. The locations of the individual patients were known, and the at-risk population was available for small areas with about 200 households known as enumeration districts (ED). Digitized boundaries for the enumeration districts were not known but a “centroid” was available.

In Openshaw's original conception, the “machine” had four components: (a) a ...