US Postal Zipcodes are based on routes (generally both sides of a street are in the same zipcode). ZCTAs are census blocks grouped into zipcode tabulation areas (ZCTAs) based on the predominant zipcode in each block. For most social science research it is acceptable to use ZCTAs and zipcodes interchangeably. However, there are more zipcodes than ZCTAs because some zipcodes do not have geography (e.g., postal box zipcodes, military zipcodes, single building/commercial & governmental zipcodes, etc.). Also, zipcodes change with time and ZCTAs are created based on the census so change only every 10th year.