This dataset represents an ongoing effort to approximate the geographic extents of 5 digit zip codes. The dataset was produced using a combination of methods and is based on several sets of source data. Methods include: 1) using local zip code polygon data obtained from counties and cities contained within these counties; 2 ) examining the 2000 Census TIGER line file's zip code attributes; and 3) using UGRC address grid quadrant boundaries to assign the zip code to segments within a boundary corresponding to a place location (city, town, places) from the postal service website and address information system (AIS). In addition, UGRC has used the locations of mailing addresses known to have valid zip codes to fine tune this dataset.