This polygon shapefile contains zip code boundaries for the United States. Data are valid from July to September, 2013. Attributes included in the data are location, area/perimeter, county names, FIPS and USPS codes, and alternate names. These data are updated quarterly using the latest feeds from the U.S. Postal Service with additional sources being used to cross-check the data. This layer provides zip code data for view and analysis in GIS and interactive web mapping applications. TTG, Inc. (2013). ZIP Code Boundaries, United States (Q3 2013). TTG, Inc. Available at: http://purl.stanford.edu/ns133qh6132