In 1993, the Maryland Department of Planning and the Maryland State Highway Administration entered into a Data Base Usage Agreement with Bell Atlantic and Data Chromatics, Inc. to develop an enhanced street address map for Maryland. Zip Code boundary area files were one of the products derived from this partnership. The resulting boundary area files were intended to improve the cartographic quality and accuracy of the zip code boundary area files derived from the U.S. Census Bureau's post 1990 Census TIGER\Line Files (based on the Census Bureau's zip code tabulation areas, ZCTAs). Subsequent iterative improvements to the Zip Code boundary area files have been made using premise address information associated with mapped parcel records as provided in the Maryland Department of Planning's MdProperty View GIS tax map and parcel record DVD product. The resulting files are meant to serve as a "good approximation" of zip codes as polygons (which in reality they are not) but are not official Zip Code maps and are not meant to be a substitute for any products offered by the U.S. Postal Service, the official source for zip code information. While there are no restrictions on their use, we do recommend that they are best used with MdProperty View. MDP makes no guarantee or warranty regarding the files. For information on the date of the data for each jurisdiction's corresponding MdProperty View edition, see the production schedule located here: https://planning.maryland.gov/Documents/OurProducts/PropertyMapProducts/Sched.pdf​