If the federal and state subsistence review process wish to consider distance to supermarkets as a definition of “rural”, then consider the USDA data for Alaska.
http://www.ers.usda.gov/publications/err-economic-research-report/err143.aspx [retrieved September 17, 2013]
Low-access census tracts
In the Food Access Research Atlas, low access to healthy food is defined as being far from a supermarket, supercenter, or large grocery store (“supermarket” for short). A census tract is considered to have low access if a significant number or share of individuals in the tract is far from a supermarket.
In the original Food Desert Locator, low access was measured as living far from a supermarket, where 1 mile was used in urban areas and 10 miles was used in rural areas to demarcate those who are far from a supermarket. In urban areas, about 70 percent of the population was within 1 mile of a supermarket, while in rural areas over 90 percent of the population was within 10 miles … Updating the original 1- and 10-mile low-access measure shows that an estimated 18.3 million people in these low-income and low-access census tracts were far from a supermarket in 2010.
Once the distance to the nearest supermarket is calculated for each grid cell, the estimated number of people or housing units that are more than 1 mile from a supermarket in urban tracts, or 10 miles in rural census tracts, is aggregated at the census-tract level (and similarly for the alternative distance markers). A census tract is considered rural if the population-weighted centroid of that tract is located in an area with a population of less than 2,500; all other tracts are considered urban tracts….