[OpenLayers-Users] Geocoding

[Stephen Woodbridge]

Paul,

Thank you for the iMaptools plug :)

Paul Spencer wrote:
> I've used a couple:
> 
> * http://geocoder.us - based on US Tiger/Line, for fee service or you  
> can get the source and build your own
> 
> * http://imaptools.com/geocode-us.html - based on US Tiger/Line, buy a  
> license
> 
> We are using navteq street data now for our maps and geocodes against  
> Tiger/Line don't align well so we currently have a home-grown solution  
> using imaptools address parser and our own postgis database.
> 
> There is some indication that PAGC (http://www.pagcgeo.org/) will  
> become more generic, supporting multiple back ends and datasets in a  
> cleaner way.  I would probably go with PAGC if that happened.

I have been working to define some changes to PAGC that we hope will 
make it much more accessible in terms of datastores and the ability to 
load North America sized datasets. It currently can only load a single 
shapefile of data which limits you to a few states or all of Canada. We 
want to be able to load all of Tiger for the US, or all of Navteq for US 
and Canada. Down the road we want to look at extending it to better 
support address parsing in other Latin language countries. PAGC has the 
right underlying technology and we are excited by the possibility of 
refactoring it to achieve these changes.

Sorry for being OT. Contact me off list if you want more information.

Best regards,
   -Stephen Woodbridge
    http://imaptools.com/

> Cheers
> 
> Paul
> 
> On 2009-10-14, at 7:09 PM, David Lozzi wrote:
> 
>> Hi Paul,
>>
>> WOW. Thanks for the insight, I've been wondering... What geocode  
>> service do you use?
>>
>> David Lozzi
>> Product Development Manager
>> Delphi Technology Solutions, Inc.
>> (978) 988-8007 x204 - www.delphi-ts.com
>>
>> Blog  -  LinkedIn  - Twitter
>>
>>
>> -----Original Message-----
>> From: Paul Spencer [mailto:pagameba at gmail.com]
>> Sent: Wednesday, October 14, 2009 5:54 PM
>> To: David Lozzi
>> Cc: users at openlayers.org
>> Subject: Re: [OpenLayers-Users] Geocoding
>>
>> This isn't a direct answer, rather I'm answering why services may be
>> different and providing some guidance on geocoding based on my
>> experience.  Don't read on if you don't care about that.
>>
>> The short answer is that differences in location returned by different
>> geocoders probably depends more on the data source being used by the
>> geocoder than the geocoder itself.
>>
>> Address parsing aside, geocoding is actually a fairly straight forward
>> process that probably uses one of two techniques:
>>
>> technique 1: linear interpolation
>>
>> * find the record that matches the requested street (a lot goes into
>> identifying the correct street, let's leave that out)
>> * find a segment of the street with a start and end address that
>> contain the requested street number
>> * find a point on the segment equivalent to where the requested number
>> is between the start and end of the line
>>
>> What is typically different here between geocoders (assuming they find
>> the same street) is the quality of the street number data (is it
>> there, is it correct, is it the right way around, is it associated
>> with the correct side of the street for odd/even etc) and the quality
>> of the geographic line segment that represents the street.
>>
>> Some services might also use some heuristic data for adjusting the
>> interpolated location from being straight linear interpolation to
>> something (that may be) more accurate.
>>
>> technique 2: exact location
>>
>> if you have tax lot/parcel/cadastral data then you can find an exact
>> match on a street address to a parcel associated with that address and
>> return the centroid of the parcel (perhaps snapped to the appropriate
>> street segment).
>>
>>
>> The other component of a typical geocoder is its ability to parse an
>> address and match it to a street segment.  This can involve a lot of
>> complicated steps and has to accommodate a seemingly infinite number
>> of ways that addresses can be written, missing address components,  
>> mis-
>> spellings of all parts, incorrect information such as incorrect zip
>> code or wrong street type, and more.
>>
>> You need to evaluate geocoders on a couple of parameters:
>>
>> * what is the source data they are using and how 'accurate' is it?
>>
>> * is it accurate enough for you vs what you are paying for it? (a
>> commercial data set might be arguably more accurate than a free one
>> for instance)
>>
>> * given how your addresses are expected to supplied, how well does
>> each service parse the address, accommodate missing, incorrect or mis-
>> spelled data and ultimately map that to the right address
>> (disregarding actual accuracy of the address)
>>
>> Typically, if you are mapping results of geocoding, you will also want
>> to ensure the geocoder is using the same source data as for generating
>> the maps to minimize the visual impact of differences in the quality
>> of the actual street vector data.  In the end, this is usually more
>> important than the physical accuracy for many use cases.
>>
>> Cheers
>>
>> Paul
>>
>> On 2009-10-14, at 5:21 PM, David Lozzi wrote:
>>
>>> Hello,
>>>
>>> What service are you using to geocode your addresses? I've looked at
>>> a couple and I've been getting different results per set.
>>>
>>> Thanks,
>>>
>>> David Lozzi
>>> Product Development Manager
>>> Delphi Technology Solutions, Inc.
>>> (978) 988-8007 x204 - www.delphi-ts.com
>>>
>>> Blog  -  LinkedIn  - Twitter
>>>
>>> _______________________________________________
>>> Users mailing list
>>> Users at openlayers.org
>>> http://openlayers.org/mailman/listinfo/users
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