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. 2020 Dec 21;15(12):e0243188. doi: 10.1371/journal.pone.0243188

Fig 1. Study participant locations across the United States.

Fig 1

The number of participants in each zip code is summarized across United States counties and displayed as a percentage of county population [35], with darker colors representing areas where participants make up a higher percentage of the county population (see legend). Reprinted from [35, 49] under a CC BY license, with permission from the U.S. Census Bureau, original copyright 2017, and the U.S. Department of Agriculture, original copyright 2013.