This polygon datalayer depicts zip code postal zones, with associated attribute data, for the Atlanta Regional Commission's (ARC) 10-county region.
ARC documentation states that:
This Theme was originally created from the national ZIP Code coverage provided by ESRI and GDT. The boundaries have been significantly changed by ARC's GIS Division using a variety of sources to improve their positional accuracy. Please note, there are some inherent problems with ZIP codes which affect the use of this Theme. Since there are overlapping areas with some of the U.S. Postal Service ZIP code data, this Theme can only show the estimated general area for many ZIP codes. Also note that some ZIP codes refer to post office boxes which only represent point locations, thus are not part of this polygon Theme.