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USPS shapefile for zip codes   dana n Jun 21, 2004
Re: USPS shapefile for zip codes   Gregory Stone Jun 21, 2004
Re: USPS shapefile for zip codes   dana n Jun 21, 2004
Re: USPS shapefile for zip codes   Jim Bash Jun 23, 2004
Re: USPS shapefile for zip codes   dana n Jun 24, 2004
Re: USPS shapefile for zip codes   Lillian Remer Oct 08, 2004
Re: USPS shapefile for zip codes   Craig Best Oct 25, 2004
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Subject USPS shapefile for zip codes 
Author dana n 
Date Jun 21, 2004 
Message
Does the USPS itself maintain a polygon shapefile of its zip code zones? If not, who does?

Thanks.

- Dana
 
  Dana N. 
   
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Subject Re: USPS shapefile for zip codes 
Author Gregory Stone 
Date Jun 21, 2004 
Message I do not believe that the USPS maintains these for the public. They may have something like this for their own internal use.

You can go to the Census Bureau's site (yes, the good old Census Bureau) and use their Zip Code Tabulation Areas. That's as good as it's going to get without buying lots and lots of GDT data.

Greg 
   
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Subject Re: USPS shapefile for zip codes 
Author dana n 
Date Jun 21, 2004 
Message Thanks Greg. 
  Dana N. 
   
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Subject Re: USPS shapefile for zip codes 
Author Jim Bash 
Date Jun 23, 2004 
Message The USPS does not maintain polygon files, in fact they don't think of ZIP codes as polys! However, every version of ArcView 3x as shipped with ZIP poly shape files by state with the additional CD data that does not get loaded on to disk by default. Most folks don't find these files and I get asked your question several times a year. I haven't looked at the 8x products but I suspect they have the same ZIP poly files.

These ZIP poly files come from GDT and the later versions have some metadata in the ArcView help. It is very important to know the date the file represents since the USPO adds and deletes files when useful for postal services. So if you have a customer/client/patient or whatever file with ZIP codes and that file represents a period of time, you either won't get a match or will get the wrong geography for some records.

I'll explain that if you want. I can lecture for an hour on the reasons I don't like ZIP codes as an areal unit of analysis. That is why we started geocoding baack in the 70s (1970s, that is:-)

Jim B
jbash@uic.edu 
   
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Subject Re: USPS shapefile for zip codes 
Author dana n 
Date Jun 24, 2004 
Message
Thanks Jim.

There's no metadata for the zip code layer I have, so I'm assuming it's old and was wondering about updates.

Do you know of any good papers/resources on the use of zip codes for geocoding, or any good articles on the finer points of geocoding? Manuals tell you how things work in ideal situations, but it ain't a perfect world.

If zip is a poor choice for geocoding by zone, what's a better one? Lots of people (and of course "lots of people" can certainly be, and frequently are, wrong) seem to think zip is the best filter we have for identifying streets.

I'm a bit disappointed in the geocoding algorithms I've "seen" (used) so far. Ideally, I'd like to use multiple layers (GDT, locally collected centerline data, city limits, zip, etc) and have more conditional control over what's going on; e.g., make a zip match "nice to have but not a deal-breaker", to use multiple road reference layers looking for the best match, etc, etc.

I've been told there's more flexibility / user-customization with geocoding in ArcGIS 9.0 (e.g. "fallback" geocoding where you can, in fact, use multiple layers). Here's hoping it works (well).


Thanks.

- Dana
 
  Dana N. 
   
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Subject Re: USPS shapefile for zip codes 
Author Lillian Remer 
Date Oct 08, 2004 
Message I've found zipcodes challenging to work with because, as Jim mentioned, they are not properly defined or documented polygons. The USPS only documents streets and addresses and only for current use. Zip codes can (and do) change, they divide, get renamed and boundaries drift. Still, there are situations (such as archival data or survey data) where zipcode is the best available geography. GDT uses USPS address books and topology to estimate zipcode polygons, using synthetic zip codes to create complete coverage (e.g., to cover national forests, state parks and such). However, they do not maintain an archive of their own historical files. I was able to purchase some older (back to 1994) GDT files from Claritas. Despite all the difficulties, I do use zipcodes in layers with other point or polygon data, but use algorithms based on modeling of the data to attribute data between different layers because most data is not homogeneously distributed within polygons. If you are interested, I've a *.pdf (of a powerpoint presentation) on using zipcodes; it's about 15 megs, but you can download it at http://www.pire.org/PRC/SSG/documents/UsingZipCodes.pdf. Good luck! - Lilli (lilli@prev.org) 
   
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Subject Re: USPS shapefile for zip codes 
Author Craig Best 
Date Oct 25, 2004 
Message Dana,

The other messages are right on regardling postal zipcode boundaries. IMHO, many people put too much faith in them because they are digital files and easy to use. The reality is that zipcodes are linear features. Any polygon representation is an approximation of the actual linear representation. The Census Bureau produces something called a ZipCode Tabulation Area or ZCTA. These were created by looking at the zipcode assigned to the actual census addresses in each census block and the most common zipcode was applied. You can download the ZCTA for each state at http://www.census.gov/geo/www/cob/z52000.html Metadata are there too.

The next release of TIGER/Line due out around the first of the year will include updated ZCTAs based using the same methodology but based on addresses from the USPS. I'm not sure that boundary files will be available for states but you can build ZCTAs from TIGER/Line on a county by county basis.