http://www.census.gov/cgi-bin/geo/shapefiles2013/main http://www.census.gov/cgi-bin/geo/shapefiles2013/main - Select ZIP code tabulation areas from the dropdown

http://www.census.gov/cgi-bin/geo/shapefiles2013/main http://www.census.gov/cgi-bin/geo/shapefiles2013/main - Select ZIP code tabulation areas from the dropdown. They're not perfect, but they're almost definitely good enough for the author's purposes. More info on how the Census Bureau creates them: http://www.census.gov/geo/reference/zctas.html http://www.census.gov/geo/reference/zctas.html (they take a surprisingly circuitous route)