Does GPS Visualizer commonly use ZIP Code centroids?

 

For a current project, I tried batch geocoding, rather than geocoding addresses one at a time. I used GPS Visualizer.

When I sorted the resulting geocoded data by ZIP Code, I was astonished to see that the exact same coordinates -- out to 6 decimal places -- were given for different addresses in the same 5-digit ZIP Code. That suggests that GPS Visualizer uses the centroids of ZIP Codes, rather than the addresses I input.

I can appreciate that not every address input may be a valid address. A coordinate provider can handle those by giving 0/0 values for long/lat, or can give some other indication that the coordinates could not be found for a given address. GPS Visualizer appears to give the ZIP centroids, rather than return no value.

Now, of course, I'm wondering about the accuracy of all the coordinates I got from GPS Visualizer, especially those where the address is the only one in a given ZIP Code.

Does anyone know if there is a setting in GPS Visualizer that will prevent it from providing centroids if it doesn't recognize the address?

I used the Yahoo setting, and furnished tab-delimited addresses: address, city, state, ZIP.

TIA.

--
Garmin DriveSmart 55 & Traffic | Garmin nüvi 250W | Garmin eTrex "yellow"

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CaseyGuy wrote:

A coordinate provider can handle those by giving 0/0 values for long/lat, or can give some other indication that the coordinates could not be found for a given address. ...Does anyone know if there is a setting in GPS Visualizer that will prevent it from providing centroids if it doesn't recognize the address?

I couldn't spot a setting when I tried it. Yahoo! and Google's geocoders do return the 'precision' of their results.

For this reason, the Batch Geocoder in GeePeeEx Editor lets you specify the degree of accuracy that you require, before the results are used. It's due for another round of 'refining', so comments welcome.

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

need more info

I'm the owner/creator of GPS Visualizer. I'm assuming you used the "Batch Geocoder" form, in which case I really have no control over what gets returned to your browser; Yahoo doesn't provide accuracy info via JavaScript. Still, can you give me more information about what you tried to do? Exactly what did your input data look like?

For best results, contact me directly using the e-mail address listed on http://www.gpsvisualizer.com/.

Yahoo & accuracy info

Hornbyp wrote:

Yahoo! and Google's geocoders do return the 'precision' of their results.

Yahoo! doesn't, if you do it via a JSON request -- unless you know something I don't?

Yahoo!

adamschneider wrote:

Yahoo! doesn't, if you do it via a JSON request

I didn't use the JSON interface; I used the XML version, but this page
http://developer.yahoo.com/common/json.html
says:

JSON versus XML
Both the XML and JSON output from the Yahoo! Web Services contain the same data; the only difference is in the format. The documentation on the Yahoo! Developer Network assumes XML output.

There's an example of the 'Precision' being returned via XML, on this page (where it says "Response Fields" :-

http://developer.yahoo.com/maps/rest/V1/geocode.html

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Yahoo + JSON

Hornbyp wrote:

Both the XML and JSON output from the Yahoo! Web Services contain the same data; the only difference is in the format.

But it's not true (anymore?) for the Geocoding service. There's definitely no "Precision" field in the only JSON output I know -- and JSON is what you must use to do it through a Web browser.

Some sites cite the following format for a Yahoo geocoding JSON request:

http://api.local.yahoo.com/MapsService/V1/geocode?appid=[appid]&location=20202&output=json

-- but that hasn't worked for quite some time. An error message is returned which reads, "json output is not supported in this service."

FYI, GPS Visualizer does have a single-address geocoder that uses XML behind the scenes and will therefore give you precision info: http://www.gpsvisualizer.com/geocode -- but it will only do one at a time, because the requests get "charged" to my server's IP address, not your browser's.

Yahoo!

adamschneider wrote:

But it's not true (anymore?) for the Geocoding service. There's definitely no "Precision" field in the only JSON output I know ... An error message is returned which reads, "json output is not supported in this service."

Maybe raising it in the Yahoo! support group (YWS-MAPS) is the answer?

He also wrote:

FYI, GPS Visualizer does have a single-address geocoder that uses XML behind the scenes and will therefore give you precision info:

Yes- I'd noted that.

BTW - I personally don't have any problems at all - but gpsvisualizer.com is very popular amongst users here and I'm sure they would appreciate a resolution.

--
------------------------ Phil Hornby, Stockport, England ----------------------               http://GeePeeEx.com - Garmin POI Creation made easy           »      

Need more info

adamschneider wrote:

... can you give me more information about what you tried to do? Exactly what did your input data look like? ...

Thanks for your personal interest, Adam. I may have deleted or overwritten the original input and output data. But I'll check to see whether I saved backup data for this particular project.

--
Garmin DriveSmart 55 & Traffic | Garmin nüvi 250W | Garmin eTrex "yellow"

Need more info

Adam,

You kindly invited me to correspond with you privately. But I've decided to reply publicly instead; I owe you a public apology.

Although I did delete the "problem" data, I was able to recreate sample input data from the orginal source. But, try as I might, I simply cannot replicate the situation I described a few days ago. In 2 attempts, with 2 different sets of data, there was not one instance of a duplicated set of coordinates from GPS Visualizer.

I can only conclude that the fault was with how I used your site originally. My most humble apologies to you and your organization. neutral

--
Garmin DriveSmart 55 & Traffic | Garmin nüvi 250W | Garmin eTrex "yellow"

no problem

It may have been something as simple as a mis-typed header; if you had fields for "address", "city", "state", and "zip", but instead of "address" you typed "addrss", it'd be ignored and you would end up with the ZIP's coordinates.

By the way, I really doubt that Yahoo will respond to complaints about the limited functionality of the JSON geocoding gateway, since it seems they don't officially support it anyway. We should consider ourselves lucky that it's available at all!

The only way I can think of that I could do any kind of accuracy checking would be to try to manually strip the street address off every datum processed, geocode the streetless version, and then check to see if it matches. And given the weird way JSON requests work anyway, I think that'd be an enormous pain and would slow things down besides...