Defining frontier areas in the United States

Demand is growing for a statistically based, nationally consistent definition of frontier territory, one that is adjustable within a reasonable range and applicable in different research and policy contexts. The need arises from Congressional mandates affecting rural health programs and from limitations of previous classification schemes. As used here, the term frontier denotes territory characterized by some combination of relatively low-population density and high geographic remoteness. Two features distinguish the methodology described here from earlier classifications. First, the approach strives for the most accurate measures of distance possible for the smallest units of geography containing population data. Travel time by car to nearby urban areas is calculated for coterminous US territory at the 1 × 1 kilometer grid level. Once frontier territory is delimited at the grid level, frontier populations may be summed to ZIP code areas, as demonstrated on the Main Map, or to census tracts, counties, or other useful geographic entities. Second, travel-time thresholds around urban areas were allowed to vary by urban-area population size. This is desirable because the effect of urban population size on adjacent rural population density is discontinuous. At any given distance from an urban area, population density increases as the size of the nearby urban area increases.