[postgis-users] US counties to Spatial_ref_sys?

[Michael Fuhr]

On Sat, Feb 25, 2006 at 05:39:27PM -0700, Darryl Watson wrote:
> I'm trying to determine which SRID to use for a given lat/long point.  
> These points will always be within United States boundaries.  I have 
> created a table with county polygon data from the US Census Bureau, 
> which is close enough for my purposes. I am using boundary data from 
> this source:
> 
> http://www.census.gov/geo/www/cob/co2000.html
> 
> I can then run a query to find which county a given lat/long point is 
> in.  Question: since I now know what US county my point is in, how can I 
> determine the SPCS zone it is in, and how to select the proper SRID from 
> the PostGIS spatial_ref_sys, for US feet?  Is there a data table out 
> there which has a county to PostGIS SRID mapping?

The following page has a spreadsheet that correlates US counties
with State Plane and UTM zones:

http://home.comcast.net/~rickking04/gis/spc.htm

You could export the spreadsheet to text and copy it into a table
in the database; that would allow you to go from lat/lon to SPCS
zone.  The next job would be to correlate SPCS zones with SRIDs.
Several mappings might be possible; for example, Colorado Central
(0502) could be any of the following:

 srid  |                 zone                  
-------+---------------------------------------
  2232 | NAD83 / Colorado Central (ftUS)
  2773 | NAD83(HARN) / Colorado Central
  2877 | NAD83(HARN) / Colorado Central (ftUS)
 26954 | NAD83 / Colorado Central
 26754 | NAD27 / Colorado Central

Unless somebody already has SPCS-to-SRID data or can suggest a
better idea, you might be able to use the proj4 files nad27, nad83,
and nad.lst to create your own entries in spatial_ref_sys or to
match SPCS zones against existing SRIDs by comparing zone names
and/or proj4 parameters.  I've been playing around with that with
some success.

Incidentally, I think I'm only a few miles north of your company;
I'm in the Denver Tech Center.

-- 
Michael Fuhr