Hi John, You are absolutely right! I have been struggling for a while to get the spatial data before 2000. The fact is, 1, I have no addresses. 2, Also, the person in ESRI told me that they do not maintain historical polygon as well. 3, I have over 5500 zipcodes scattering between year 1992-2006 to look at.
Since for those about 440 zips that I could geocoded, there are three situation could be: 1, obsolete 2, point zip that couldn't be mapped in polygon 3, valid, but doesn't exist in ESRI 2007 database So one of my approaches now might be: 1, choose one year as spatial reference data (probably your USPS ZIP product instead of ESRI). 2, get all centroids of the ZIP on map 3, get latitude and longitude for those point zips enclosed in polygon zips. 4, combine two sets of point features in one layer, process interpolation Therefore, I get rid of those "obsolete" zips in my analysis. But where can I get the latitude/longitude for step3? You should have these in your database, correct? Thanks, Ivy On Wed, Mar 4, 2009 at 11:18 AM, Maps.Huge.Info (Google Maps API Guru) < [email protected]> wrote: > > The Census ZCTA polygon database has been updated only a couple of > times. I believe there is a 1990, 2000 and "current" version which is > really 2002. In order to "fill in the blanks" as you put it, you'll > need some historical zip code data from the USPS, I personally think > you're going to have a difficult time finding it. That data is fairly > perishable and most companies who use zip code data only care about > the most current, not what it was a year ago. > > I suppose if you had a list of addresses from the period you're > interested in with their existing zip codes, geocoded them without the > zip code and then used a convex hull algorithm to convert the data > into a polygon you'd have something close, the problem would be > figuring out the borders where one zip code lies next to another. If > you're only concerned with a couple of zip codes, you could easily do > it by hand, using the best spatial tool ever created, your brain. > Doing so automatically with a program would be quite a bit more > complex. > > It could be that ESRI has a historical zip code polygon archive, you > might contact them to see what they have and what it will cost. > > -John Coryat > > http://maps.huge.info > > http://www.usnaviguide.com > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google Maps API" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/Google-Maps-API?hl=en -~----------~----~----~----~------~----~------~--~---
