-------- Original Message --------
Subject: Re: Get the skinny - census data query by zip code
Date: Thu, 18 Oct 2007 18:17:57 -0400
From: Bob Kibbee <[log in to unmask]>
To: Maps, Air Photo & Geospatial Systems Forum <[log in to unmask]>
Hi All,
It's a little more complicated, I think. Postal Zip Codes are groups
of addresses, not areas or polygons, and so can't have center points.
The Census Bureau creates what they call Zip Code Tabulation Areas
(ZCTAs) to give the illusion of a Zip Code polygon. They're based on
the address networks, but not the same. The ZCTAs are built from
census blocks and do have centroids and areas. The best discussion
I've found is at the cleverly named:
http://exchange.manifold.net/manifold/manuals/5_userman/mfd50Zip_Codes_are_Not_Areas.htm
The "official" ZCTA site is: http://www.census.gov/geo/ZCTA/zcta.html
(not updated since 2001) and the flashier and more helpful brochure:
http://www.census.gov/prod/2001pubs/mso01zcta.pdf
The appeal of the ZCTAs is that they correspond fairly well to the
address networks of the Post Office Zip Code (good enough for
marketers), and have aggregated census block data associated with
them. So they provide a geographic unit that is usually a little
larger than MCD (for 5 digit ZCTAs) or larger than counties (3 digit
ZCTAs) with SF1 data. In urban areas they might provide an alternate
way to construct "neighborhoods."
One possible problem with the SF3 sample data used in the reports
(which the site is very upfront about) is that this data isn't
summarized for blocks by the census, so the sample data is being
"developed" from some other geographic unit(s), either block groups
or tracts. This can be a little iffy, as Angie suspects.
But it's a engaging presentation, and fun to play around with.
Bob
At 12:51 PM 10/18/2007, you wrote:
>-------- Original Message --------
>Subject: Re: Get the skinny - census data query by zip code
>Date: Thu, 18 Oct 2007 11:24:24 -0500
>From: Toby Main <[log in to unmask]>
>To: Maps, Air Photo & Geospatial Systems Forum <[log in to unmask]>
>
>
>
>Just remember that ZIP codes are purely for the convenience of the
>postal service. Business types love them, but they are often not
>particularly useful for any other purposes. Census tracts are a far
>more rational demographic unit.
>
>TM
>
> ----- Original Message -----
> From: "Maps-L"
> To: [log in to unmask]
> Subject: Get the skinny - census data query by zip code
> Date: Thu, 18 Oct 2007 08:53:01 -0500
>
>
> This is a pretty neat census data web site. I don't know of it's
> reliability or anything ... but thought I'd share it anyway.
>
> After entering a main zip code and getting the first page of results ,
> there's a table toward the bottom where one can enter zip codes of 19
> other locations and get comparison information. The results page also
> includes a map showing the geographic center of the area queried.
>
> Angie
>
> www.ZIPSkinny.com
>
>
>--
>Want an e-mail address like mine?
>Get a *free e-mail *account today at www.mail.com
><http://www.mail.com/Product.aspx>!
Bob Kibbee
Map & GIS Librarian
Instruction, Research & Information Services (IRIS)
B17 Olin Library, Cornell University
Ithaca, New York 14853-5301
voice 607-255-9566 / fax 607-255-3609
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