[postgis-users] extracting zipcode bundaries from tiger2005sebasedata

[Dan Putler]

Hi All,

There are a couple of interesting points on this matter from the  
Census Bureau's FAQ. The relevant FAQs are questions 17 and 18. The  
link is:

http://www.census.gov/geo/www/tiger/faq-index.html

I am part of a small group working on creating an open Canadian  
Forward Sortation Area (FSA) polygon layer. An FSA is Canada Post's  
equivalent of a US five digit zip code. In urban areas we are  
attempting to use the boundary road segments for an FSA from the  
recently released Statistics Canada 2006 Road Network File (the  
Canadian counterpart to the TIGER/Line road layer). However, these  
produce boundaries with gaps. So far we haven't found a solution that  
doesn't involve hand digitalizing some of the boundary segments, and  
my reading of the TIGER documentation suggests that the same problem  
will occur when TIGER/Line data is used to create zip code polygons.  
One important difference between Canadian FSAs and US zip codes is  
that FSAs are assigned based on spatial polygons, while this is not  
the case for US zip codes. The problem with Canadian FSAs is that  
things other than roads are used as boundaries in a number of instances.

Dan

On 18-Oct-06, at 9:50 AM, Stephen Woodbridge wrote:

> Dylan Beaudette wrote:
>> Hi everyone,
>> On the GeoServer website there are excellent directions on how to  
>> extract specific information from the tiger2005 base data. However  
>> there are no instructions covering the extraction of zipcode  
>> boundaries. Does anyone know of a good way to go about doing this  
>> in postgis ? I already have the tiger2005se database setup.
>
> Dylan,
>
> Here are a couple of possible solutions.
>
> A. this is how the census does it
>
> 1. create all the block polygons
> 2. assign each block polygon a zipcode based on analysis of the  
> zipcodes on the inter edge of the block polygon
> 3. union all the block polygons for each unique zipcode
> 4. look for small islands where a block is surrounded by other  
> other zipcodes and deal with it.
>
> B. probably a bad option
>
> 1. collect all edges that belong to a zipcode excluding '00000'
> 2. pass this to buildarea() function.
> 3. this will probably fail because of gaps in the edges where  
> zipcodes are not assigned.
>
> C. download the zcta polygons for Census, inspite of the fact they  
> are based on Tiger2000 files.
>
> -Steve
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