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How is Map-able Carrier Route and ZIP Code Boundary Data Created?

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What Exactly is a ZIP Code….or a Carrier Route?

The ZIP Code and carrier route coding system was specifically developed by the United States Postal Service (USPS) in order to make mail delivery more efficient.  This means that what the average person refers to as a “ZIP Code”, is actually a collection of addresses that have the same 5-digit code assigned to them. The USPS then further splits up each of these ZIP Codes into smaller blocks of addresses: carrier routes. A carrier route literally corresponds to the group of addresses that an individual mail service employee is responsible for delivering to each day.

There are roughly 43,000 ZIP Codes in the US.  These are divided into approximately 600,000 unique carrier routes with, on average, 15 carrier routes per ZIP Code.  Fifty percent of these are PO Box-based carrier routes which do not have actual delivery areas.

ZIP Codes and carrier routes do not tie in to any other US geography. Because of this, they frequently cross city, census tract, county and even state boundaries. The USPS does not provide maps or map data for ZIP Codes and carrier routes. Businesses looking for postal map data to inform their sales territory tracking, direct marketing and other initiatives have to turn to private map data compilers for this information.

From the Ground Up: Combining Addresses to Make Carrier Route Polygons

The protocol a map data compiler uses to create ZIP Code and carrier route boundaries is of utmost importance in determining the accuracy of the final product.  Our aim is to provide you with an understanding of the Maponics process.  As you can imagine, some of the relevant information is proprietary, and thus not publishable. But we will be as descriptive as we can without giving away trade secrets.

The first step in creating ZIP Code and carrier route boundaries is to match a) a database of actual addresses tagged with the correct postal information to b) a map-able database of US streets.  To do this, we start with the USPS Postal AIS (Address Information Systems ) Database.  This data is released quarterly by the USPS and contains 45-50 million individual address records, each with a street address, ZIP Code, ZIP +4, and carrier route. We match this AIS dataset against a nationwide database of streets containing over 100 million individual street segments. Because these postal and the street datasets have been created for very different purposes, combining them accurately requires sophisticated algorithms.

Once each address has been assigned to the correct street segment, we then take all of the street segments with addresses that have the same carrier route assigned to them and combine them.  This forms a polygon that represents the entire geographic area covered by that carrier route.

That’s the simplified version.  Many issues arise related to the original data and the Maponics postal data developers are constantly quality checking for discrepancies.

 From the Carrier Routes, the ZIP Codes Are Built

Once these carrier route polygons are created we then combine them to build our ZIP Code polygons.  This ensures that our carrier route boundaries always synch with our ZIP Code boundaries, and never cross into neighboring ZIP Codes.

Learn more about our ZIP Code and Carrier Route Map Data. Or, find out the difference between ZCTAs (US Census provided ZIP Code approximations) and ZIP Codes, and browse all of our posts related to carrier route boundaries and ZIP Code data.