In response to the US Postal Service's zip code changes in West Jordan and Cedar City, effective July 1, 2008 [see detailed description], AGRC has updated the SGID's 5 digit zip code polygon feature class SGID.U024.ZipCodes to reflect the new changes. The updated dataset is now available on the SGID ArcSDE Database Server and on the SGID FTP site. AGRC is committed to updating zipcode data as the US Postal Service makes its infrequent changes -- usually in repsonse to increased development or population increases.

Please keep in mind that, while most of us think of zip codes as polygon geographic features, zip codes are really just simple mechanisms for sorting mail so that it arrives at the correct post office for distribution and in reality, the US Postal Service assigns zip codes at the block face level and only for streets that receive mail delivery. In other words, zip codes are address range based, not areal in nature.

For the SGID.U024.ZipCodes polygon GIS layer, AGRC has constructed a statewide zip code layer that approximates the boundaries at which the the real world linear-based zipcodes change. In reality the left side (ZIP_LEFT) and right side (ZIP_RGHT) zip code attributes carried by the U024.StatewideStreets are a much better representation of zip codes as geographic features. look for the U024.StatewideStreets dataset and geocoding address locators based on this dataset to be updated in the next couple days with an accompanying post to the GIS Portal.

Note: while the polygon zip code feature class definitely has its applications, representing zip codes as polygons has several disadvantages. Two of these disadvantages are:

• Wherever mail is not delivered to addresses (e.g. rural routes & and areas where only post office box delivery is offered), the zip code polygons are just guesses as to how the zip code system would be extended if mail was delivered to these rural areas
• Where a zip code polygon boundary follows a street centerline, it is impossible to know what zip code is to be found on a specific side of the street. The zip code on the left and right side of the boundary along the centerline could be the same or different. This information is, however, found on the left side (ZIP_LEFT) and right side (ZIP_RGHT) zip code attributes carried by the U024.StatewideStreets.