The Zip Codes data set is an attempt to represent mailing address zip codes as single contiguous polygons. This is not unique to this particular data set. All polygon zip code data sets share this conundrum.
Zip code polygons are used as a geographic aggregation tool. Many types of data are aggregated to zip code including demographic data.
US Census Bureau
unknown, some adjustments have been made to parcel boundaries
Florida Albers HARN
po_name state sumblkpop pop2001 zip descript latitude longitude