1. Association of American Geographers (AAG), 1710 16th Street, NW, Washington, DC 20009, USA.
2. National Institute on Drug Abuse, National Institutes of Health, Bethesda, MD 20852, USA.
3. Department of Geography and Geographic Information Science, University of Illinois at Urbana–Champaign, Urbana, IL 61801, USA.
4. Office of Behavioral and Social Sciences Research, National Institutes of Health, Bethesda, MD 20892, USA.
5. Department of Geography, University of California, Santa Barbara, CA 93106, USA.
6. Division of Cancer Control and Population Sciences, National Cancer Institute, Rockville, MD 20852, USA.