[cgiapp] Re: [OT] Searching for a db of American Localities and Postcodes

[Mark Stosberg]

On Fri, 10 Jul 2009 11:07:20 +1000
Ron Savage <ron at savage.net.au> wrote:

> Hi Folks
> 
> For a home-use module, I use American postal data from ZipCodeWorld
> 
> http://www.zipcodeworld.com/index.htm

I have dealt with this issue on a number of projects over the years.
The most recent "open source" version of the data is US Census data from
from a few years ago. However, New postal code databases are released
*every month* with new updates. It's my sense you need fresh data about
every 3 to 6 months to stay very current. 

It does seem like it should be public data, but it's not now. I have
used at least 3 Zipcode vendors over the years. I quit using TPSnet,
although I don't recall why now.

I'm currently using this vendor:
http://www.zip-codes.com/

But they are not perfect, either. In a recent update, I had the
geo-spatial data *disappear* in some zipcodes. The explanation was that
it was determined that the coordinates needed to be recalculated, but
weren't available yet. In that case, I would expect the vendor to do the
service of continuing to ship the older slightly less accurate version
rather than no coordinates at all.

Also note that there is sometimes a lag time between when new zipcodes
are published and when the coordinates for the zipcodes are available.
This vendor has been been shipping zeros for the coordinates in those
cases.  Some other vendor (I'm not recalling which one now), "cheats" by
using a post office location as the center of zipcode, until the
official coordinates are published. I think that's actually the better
behavior, because at least people in those zipcodes can search for
themselves with *some result* rather than waiting months before the
zipcode is useable in geo-spatial searches at all.

Because I have learned not to trust Zipcode vendors, we've written our
own kind of zipcode update "diffing" tool, so with each update I can get
my own report of which zipcodes have been added and removed, as well as
which ones have missing geo-spatial data. Right now that tool is
specific to our data model storage, so it's not suitable for release.

If you are also tracking zipcode updates for a project, I do recommend
you QA the published updates like this... In my experience there are
nearly always some anolomies that need reviewed and sometimes manually
addressed.

    Mark





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