Understanding and mapping ZIP Codes

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If you live or frequently send mail to the United States, then you probably understand that one of the most important components of the address is getting the ZIP code correct in order to have your mail successfully arrive at the intended address.  The city or community that you list is not as important as long as the ZIP code is correct.  Standing for “Zone Improvement Plant”, the Census Bureau defines ZIP code as:

A Zone Improvement Plan (ZIP) Code is the numerical code assigned by the U.S. Postal Service to designate a local area or entity for the delivery of mail. ZIP Codes may consist of 5, 7, 9, or 11 digits, and may refer to a street section, a collection of streets, an establishment, a structure, or a group of post office boxes.

Downloading GIS ZIP Code Data

There are some free sources for downloading ZIP Code data.

The US Census Bureau offers what is known as ZIP Code Tabulation Areas (ZCTA) which is a shapefile format polygon file of the generalized ZIP Code service areas.  There is a boundary file for the 2000 Census but the 2010 Census data for ZIP Codes is offered as an ASCII file via the Gazetter page.  The downloable 2010 ZIP Code file contains the five digit ZIP code,   2010 Census population and housing counts, and latitude/longitude values.

The ZIP Code Database Project offers public domain data based on the 200 census for ZIP Codes in either CSV or MySQL dump format.  The databases include geographic coordinates.


Some have looked at the numbering scheme used for ZIP Codes.  Ben Fry created an basic application called zipdecode that shows the location of all the ZIP codes in the United States.  You can type in a ZIP code and the location and name of that location will show up on the map.  If you hold down the shift key and type the first number of the ZIP code, the region of the United States is highlighted.  For example the number “9” highlights California, Oregon and Washington.  Highlighting through the entire set of nine numbers sequentially (1, 2, 3 etc.) provides an interesting manual animation of how the ZIP codes are laid out across the country.

Ben Fry's ZIP Code Map: Zipdecode.
Ben Fry’s ZIP Code Map: Zipdecode.

US ZIPScribble Map

Robert Kosara took this idea a step further and created the US ZIPScribble Map.  His premise was to “connect the dots”.  He connected all the ZIP code point locations in ascending order and color coded the map to see if the ZIP codes adhered to state boundaries.  He found that some ZIP codes did adhere to state boundaries and others did not.

Robert Kosara's Zip Scribble Map
Robert Kosara’s ZIP Scribble Map


USPS Making the Case for GIS
With the fiftieth anniversary of the ZIP Code, the Office of the Inspector General at the USPS has release a paper exploring ways to improve the ZIP code. The report, entitled “The Untold Story of the ZIP Code”, recommends linking the USPS address database with GIS to create a more efficient ZIP Code system.

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