Date:         Wed, 16 Aug 2000 18:13:04 -0600
Reply-To:     Jack Hamilton <JackHamilton@FIRSTHEALTH.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Jack Hamilton <JackHamilton@FIRSTHEALTH.COM>
Subject:      Re: convert census tract to zip or vice versa?
Comments: To: burleym@WSIPP.WA.GOV
Content-Type: text/plain; charset=us-ascii

SAS doesn't (well, SAS/GIS might, I don't know, but base SAS doesn't).

There are commercial sources for this information, and there are at
least three algorithms for determining ZIP centroids:

1) Geographic center, maybe not a good idea if the ZIP's population
   isn't evenly distributed.  It might be in the middle of a lake.

2) Sampled center, the lat/lon of an actual populated place in the
   ZIP code.  If you ask for the lat/lon 5 times using this method,
   you might get 5 different answers, but they will all correspond
   to real addresses, and heavily populated locations will be
   returned more frequently.

3) Population weighted center, the lat/lon weighted by population.
   This is probably what you want for calculating distances, but
   again the location might be in the middle of a lake.

ZIP codes can be fairly large.  I don't know exactly how large
they can get, but it wouldn't surprise me to find a ZIP code that
covers a thousand square miles (in a sparsely populated area).
Does anyone know what the largest ZIP code is?



--
JackHamilton@FirstHealth.com
Development Manager, Technical Group
METRICS Department, First Health
West Sacramento, California USA


>>> "Burley, Mason" <burleym@WSIPP.WA.GOV> 08/16/2000 4:42 PM >>>
You may create an allocation factor (using population, land area, or
housing units) between two overlapping geographic divisions based on
1990 census data using the following web site:
[http://plue.sedac.ciesin.org/plue/geocorr/]

Since this generates factors based on 1990 data, you may miss some newly
created zip codes.

Now a question for the list:  I have obtained the formulas to calculate
distances between two places using latitude and longitude.  Now I need
to find a file with zip codes and corresponding latitude/longitudes.  Do
I have to purchase this data, or does SAS have a facility for this?

Regards,

Mason Burley
Washington State Institute for Public Policy

-----Original Message-----
From: Drew Spencer [mailto:DrewSpen@IMAGIN.NET]
Sent: Wednesday, August 16, 2000 4:02 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: convert census tract to zip or vice versa?


Folks,

Anyone know how I can convert census tract to zip or vice versa?
I am using SAS.

--
Kent Andrew (Drew) Spencer
MailTo:DrewSpen@Imagin.Net


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