[OpenLayers-Users] Geocoding

[David Lozzi]

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
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From: David Anguiano [mailto:fenixxiii at gmail.com] 
Sent: Thursday, October 15, 2009 3:30 PM
To: David Lozzi
Subject: Re: [OpenLayers-Users] Geocoding

 

 

2009/10/15 David Anguiano <fenixxiii at gmail.com>

 

2009/10/15 David Anguiano <fenixxiii at gmail.com> 

	 

	but please do not send Messages to this post, thanks

	2009/10/14 David Lozzi <dlozzi at delphi-ts.com> 

		 

		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: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
<http://www.delphi-ts.com/> 
		>
		> Blog  -  LinkedIn  - Twitter
		>
		> _______________________________________________
		> Users mailing list
		> Users at openlayers.org
		> http://openlayers.org/mailman/listinfo/users
		
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