Zip+4's are really line segments. The weighted centerpoint of these is what's delivered normally for Zip+4 geocoding and analysis purposes. I think there are normally a group of about 8-10 households in a zip+4.
Additionally, in a zip code, the USPS thinks about delivery in terms of Carrier Routes. Each postal carrier follows the route and delivers the mail. If you do a bulk mailing to everyone in a carrier route, than you get a discount. Each Tiger segment has a carrier route associated with it. Several companies take these Carrier Routes and make polygons. There are several methods of computing the polygons - some do it to the street centerline, others take it to a rear property line. This website goes into a little more detail about carrier routes, discounts and sub zip code geography etc. http://www.carrierroutes.com/ Hope this helps. -Lynwood On Fri, Oct 15, 2010 at 1:22 PM, Edward Vielmetti < [email protected]> wrote: > Are +1 boundaries sane to compute, if you had all of the +4 points? > I'm wondering > if there are sub-zipcode boundaries that make any sense, in the same way > that > the first 3 of the zip encodes a region that is usually mostly contiguous. > > On Fri, Oct 15, 2010 at 1:07 PM, Ian White <[email protected]> wrote: > > Does not exist for free. ZCTA are stylized zips and are not updated, but > > avail through census. That is free. Anything else is $$. +4 is point data > > and easily overkill unless you want deliverability > > > > Ian White :: Urban Mapping Inc > > 26 O'Farrell Street Suite 310 :: San Francisco CA 94108 > > T.415.946.8170 :: F.866.385.8266 :: urbanmapping.com/blog > > ________________________________ > > From: [email protected] < > [email protected]> > > To: [email protected] <[email protected]> > > Sent: Fri Oct 15 12:04:40 2010 > > Subject: [Geowanking] zip+4 shapefiles > > > > Hi, > > > > > > > > I was wondering if anyone knows where I can find zip+4 shapefiles (e.g. > > polygons). The few companies that I found who supposedly sell this data > > have mostly empty entries for at least half of the zip+4s. Is there a > > direct (free) government source for these shapefiles? Thanks, Armand > > > > > > > > > > > > > > > > _______________________________________________ > > Geowanking mailing list > > [email protected] > > http://geowanking.org/mailman/listinfo/geowanking_geowanking.org > > > > > > > > -- > Edward Vielmetti, Ann Arbor, MI 48104 > > Google Voice: +1 734 330 2465 > Work: http://annarbor.com/vielmetti > Web: http://vielmetti.typepad.com > Thursday a2b3 lunch: http://groups.yahoo.com/group/a2b3/join > > _______________________________________________ > Geowanking mailing list > [email protected] > http://geowanking.org/mailman/listinfo/geowanking_geowanking.org > -- *LYNWOOD BISHOP, PRESIDENT* MapLarge, Inc. <http://maplarge.com/> P.O. BOX 8482 ATLANTA, GEORGIA 31106 DIRECT: 404.797.3408 FAX: 678.298.8702 Email: [email protected] http://www.maplarge.com
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