I'm confused, why not?
David Lozzi Product Development Manager Delphi Technology Solutions, Inc. (978) 988-8007 x204 - www.delphi-ts.com <http://www.delphi-ts.com/> Blog <http://www.delphi-ts.com/blogs/lozzi> - LinkedIn <http://www.linkedin.com/in/davidlozzi> - Twitter <http://www.twitter.com/davidlozzi> From: David Anguiano [mailto:[email protected]] Sent: Thursday, October 15, 2009 3:30 PM To: David Lozzi Subject: Re: [OpenLayers-Users] Geocoding 2009/10/15 David Anguiano <[email protected]> 2009/10/15 David Anguiano <[email protected]> but please do not send Messages to this post, thanks 2009/10/14 David Lozzi <[email protected]> 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 <http://www.delphi-ts.com/> Blog - LinkedIn - Twitter -----Original Message----- From: Paul Spencer [mailto:[email protected]] Sent: Wednesday, October 14, 2009 5:54 PM To: David Lozzi Cc: [email protected] 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 <http://www.delphi-ts.com/> > > Blog - LinkedIn - Twitter > > _______________________________________________ > Users mailing list > [email protected] > http://openlayers.org/mailman/listinfo/users _______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
_______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
