The National Health Service in Britain is undergoing far-reaching changes. While District and Regional Health Authorities are currently merging, professionals agree that primary health care is most efficiently managed at the local level. This paper uses geographical information systems (GIS) capabilities to identify a nested hierarchy of localities for the management of primary health care in West Sussex, England. GIS coverages were developed which contained key criteria for defining local areas, including nodes or focal points of service provision, edges which act as physical or psychological barriers to movement, districts such as official administrative areas and interaction criteria such as journey to work, school and family doctor (GP) surgeries. Central to the derivation of the localities was a large matrix of patient to GP flows based on postcoded data. Once managed, these data revealed clear geographical patterns of patient to GP allegiance. A large-scale field survey obtained supporting information on the perception of areas from local residents.