[postgis-users] Geocoder (from extras)

[Johnathan Leppert]

Do you know what the status of the PAGC project is? Is it still under active
development? The last post was in 2008.

On Sat, May 7, 2011 at 5:00 PM, Stephen Woodbridge
<woodbri at swoodbridge.com>wrote:

> Stephen,
>
> In a geocoder I wrote in 2000, I mapped city, state and/or zipcode into a
> list of counties, then only searched those counties. This greatly reduced
> the 3300 counties in Tiger to a small handful that needed to be searched.
> The FIPS-4 document has a mapping of all place names to counties. Zipcodes
> are easier to handle because you can just index the records with zipcodes
> but if you wanted to widen the search, then map the zipcode to a place name
> and then to counties.
>
> My first thought was to use inherited tables where each state or state
> equivalent is in a separate table and filter the tables by the state name of
> abbreviation. It sounds like you might be already doing something like this.
>
> I think trigrams would provide some benefits. I have used double metaphone,
> but only used the first code for fuzzy searches because this is a better
> phonic search key than soundex in my opinion because it matches thinks that
> sound alike even if they do not start with the same letter. Since I used it
> as a key I only used the first 4 characters of the metaphone code.
>
> I wrote my own tiger geocoder in C and have since abandoned that in favor
> of PAGC. PAGC has just recently refactored the code to support SQLite as a
> datastore and has had some work done to support Postgresql in addition to
> the previous support for Berkeley DB. One idea that I had was that with
> appropriate support for database backing stores, that the PAGC library might
> be able to be wrapped in a stored procedure which would then provide a high
> quality and high performance geocoder in the database.
>
> Here is an instance that I created using SQLite as the backing store and
> Tiger 2010 data:
>
> http://imaptools.com:8080/geocode/
>
> The single line parsing is broken at the moment, I have a ticket to look
> into that and hope to have it resolved shortly.
>
> PAGC project can be found here:
>
> http://www.pagcgeo.org/
>
> Regards,
>  -Steve
>
>
>
> On 5/6/2011 10:36 PM, Stephen Frost wrote:
>
>> * Johnathan Leppert (johnathan.leppert at gmail.com) wrote:
>>
>>> Ok, I have it working, but it's very very slow. It takes about two
>>> seconds
>>> to geocode a single record. This isn't very realistic for large datasets.
>>> Anyone have any ideas on possible optimization? It appears to have
>>> created
>>> proper indexes on all the tables.
>>>
>>
>> Yeah, there's a few things I've been working on.  For one, a lot of the
>> time is spent planning that massive query at the heart of the geocoding,
>> when it really doesn't need to be re-planned for every query.  It's done
>> the way it is currently because the tables are partitioned up by state.
>> I've got someone working on simply splitting that query up to be 53 (or
>> however many...) queries, one for each state/territory, which will allow
>> them to be planned once and then the plans re-used inside the same
>> session.  That should improve things.
>>
>> I've also been looking into using trigrams for things instead of the
>> current indexes..  I think they're perform better with regard to speed,
>> just need to make sure it still returns good results, etc..
>>
>> I'm very interested in anyone else working on this and any suggestions
>> people have for how to improve it..  I've not been able to work on it
>> much recently and while I've tried to delegate it to others, it's a
>> pretty complex system which is, in particular, hard to test well..
>>
>>        Thanks,
>>
>>                Stephen
>>
>>
>>
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-- 
*Johnathan*
Software Architect & Developer
Columbus, Ohio
*Follow me on Twitter: @iamleppert <http://twitter.com/#!/iamleppert>*
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