Pharmacy deserts? using GIS (Geographical Information Systems) to map potential disparities in US pharmacy access

Introduction: “Deprivation amplification,” the pejorative effect of environmental disparities on individual level disparities, is associated with poor access to health-care and food. Pharmacy access may be subject to analogous forces. Small population-level studies suggest a scarcity of pharmacies in rural and poor areas, but no large-scale spatial analysis project has been completed. We use GIS to investigate continental US pharmacy access by road.

Methods: Geospatial techniques, including geographic information systems (GIS), permit us to assess distance as experienced by pharmacy customers, quantifying it as transportation along roads. County level data was obtained from Census 2010 and the North American Roads network (ESRI), and was mapped with ArcMap10.1. Pharmacy locations were mapped using the Business Analyst 2011 geodatabase. Population weighted centroids (PWC) were calculated based upon census tract population to provide an average location of county inhabitants and mapped to the road network for 3089 counties. Pharmacies within 1 mile by road of the PWC, “walking distance,” were counted as accessible for counties with lowest car ownership (>2 standard deviations below mean). For all other counties, accessible pharmacies were within 10 miles by road of the PWC, or “driving distance."

Results: Maps of accessible pharmacies were produced. Number of pharmacies accessible to the PWC ranged from 0 in many rural counties, to 721 in Manhattan, NY. 457 counties had no accessible pharmacy.

Conclusions: Counties without accessible pharmacies are potential “pharmacy deserts.” Many counties without pharmacy access are adjacent, suggesting spatial clustering, potentially leading to additional increases in travel distances.