Accessibility refers to the relative ease by which the locations of activities, such as work, shopping and healthcare, can be reached from a given location. Access varies across space because of uneven distributions of supply and demand (spatial factors), and also varies among population groups because of their different socioeconomic and demographic characteristics (nonspatial factors). Taking healthcare access for example, spatial access emphasizes the importance of geographic barrier (distance or time) between consumer and provider, whereas nonspatial access stresses non-geographic barriers or facilitators such as social class, income, ethnicity, age, sex, and so forth. Since the 1960s, health policymakers in the United States have attempted to improve health care for the citizenry by considering aspects of both spatial and nonspatial factors. Such efforts are exemplified in designations of Health Professional Shortage Areas (HPSA) and Medically Underserved Areas or Populations (MUA/P) by the U.S. Department of Health and Human Services (DHHS), for the purpose of determining eligibility for certain federal health care resources. The DHHS is considering consolidating the HPSA and MUA/P designations into one system because of their overlapping criteria (U.S. DHHS, 1998). See guidelines at http://bphc.hrsa.gov/dsd (last accessed April 1, 2004).