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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: [gislist] Zip Code Boundaries |
| Date: |
10/16/2003 07:35:01 PM |
| From: |
Robert Heitzman |
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ZCTA's are probably the most stable over time but as noted ZIP areas don't
really exist.
Depending on the size of the area it may be managable to have a program map
some ZIPs you know you will get to ZCTAs just to get some value to store in
the DB. With little effort you should quickly get to 99% acceptance of the
user supplied data.
Something to look out for is I don't think ZCTAs cover 100% of the "ground".
Or there are some default ZCTAs that the unaccounted for areas are lumped
into.
Using other Census areas have the problem of the client having any idea of
what area they live in.
Other options are to use geocoding of addresses and come up with lat/long
points for each client record. These points can be summarized over any area
scheme you want to come up with.
Address geocoding has a less than 100% address to point in space success
rate as the user/client can get more creative than a computer can handle
when providing address data. There are some commercial services that have
high success rates by using multiple methods to get an answer. A lot depends
on how close you really need to get and how important misssing 10-20% of the
records is to your application.
Most GIS tools have address geocoding features, some supplied, some a little
extra. You will need some DB of addresses. the Census TIGER data (free) can
be used with the base ArcView/ArcGIS tools and you will get 70-85% of your
addresses coded within 50-100 feet of the "real" address most of the time,
especially in urban settings.
There are commercial services you can send addresses to and they will return
lat/long data. For a big/long term project this may be the best way to go.
I wouldn't bother with commercial ZIP codes areas. If you are going to spend
money I'd suggest you go with the address geocoding. Privacy may be an issue
to consider if you publish any data about the individual points.
>Thanks for the help. I agree and realize that zip code boundaries are not
>the way to go. I did not realize that there were no actual boundaries for
>zips. My problem is trying to convince no GIS people (physicians and
>hospital administrators) that census geography is a more accurate way to
>portray data. Since the non-GIS people can visualize and recognize a zip
>code 28202 (because they use it everyday) rather than census tract 201.04,
>my job to educate them has not gone well.
>
>>I am trying to align Zip Code Boundaries in North Carolina to actual
>>streets, rivers, etc. Do zip codes follow the same rationale as census
>>tracts? I know that the boundaries change frequently, but I cannot find a
>>free source that shows the accurate physical locations. HELP!
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