The H-GAC ZIP code coverage includes polygons and their attributes for Harris, Fort Bend, Brazoria, Galveston, Chambers, Liberty, Montgomery, Waller, Austin, Colorado, Matagorda Wharton and Walker County. It was primarily created from the census 2002 ZIP code boundary data with secondary source data coming from Centerpoint ZIP code, Esri 2009 ZIP code, address point data from centerpoint and counties, CRIS ( Carrier Route Information System) data, US Postal Services Online site ( Look up a ZIP code) and parcels. Must Not Overlap and Must Not have Gaps topology rules have been used in order to create an accurate ZIP code layer.

The layer represents physical ZIP codes and a few PO BOX ZIP codes are included rural areas . PO BOX ZIP codes can be identifying by "zip_type" field in the attribute table.