This paper describes a functional approach to the definition of rural populations for purposes of rural health care research. Rather than define "rural" directly, we created a definition of urban populations and our research target became the non-urban component. Using Geographic Information Systems technology, isochrones (drivetime zones) were created that attached suburban populations to urban centres and mapped non-urban populations into rural hospital catchment areas. For population-based analyses, we have proposed a methodology for constructing catchment areas attached to Rural, Regional and Metropolitan services. We have developed a model for calculation of travel time for patients required to travel for care. We successfully applied these methodologies to the disparate regions of rural Alberta and Northern Ontario in 2 papers that investigated the delivery of rural surgical services. This methodology represents a durable and portable designation of "rural" with potential for research applications in other areas of health research. By defining "urban" rather than "rural," we avoided many of the methodological conundrums in this research field.