Google Maps API Tutorial

© 2006, 2007, 2008, 2009 Mike Williams

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Geocoding with error handling

The mechanics of geocoding without error handling are well explained in the official documentation but the examples shown there do not include error handling.

Geocoding requests can fail for a variety of reasons, so it's a good idea to check for successful completion before attempting to plot markers using the returned information.

It's also helpful to display the failure reason to your users, where possible, otherwise your users might waste their time doing things like trying to guess the correct spelling of "Sauchiehall Street, Glasgow, UK", if the problem isn't the spelling but the fact that you've used up youir geocoding quota already.

What you can do is to set up an array like this

 var reasons=[];
 reasons[G_GEO_SUCCESS]            = "Success";
 reasons[G_GEO_MISSING_ADDRESS]    = "Missing Address: The address was either missing or had
                                      no value.";
 reasons[G_GEO_UNKNOWN_ADDRESS]    = "Unknown Address:  No corresponding geographic location
                                      could be found for the specified address.";
 reasons[G_GEO_UNAVAILABLE_ADDRESS]= "Unavailable Address:  The geocode for the given address
                                      cannot be returned due to legal or contractual reasons.";
 reasons[G_GEO_BAD_KEY]            = "Bad Key: The API key is either invalid or does not match
                                      the domain for which it was given";
 reasons[G_GEO_TOO_MANY_QUERIES]   = "Too Many Queries: The daily geocoding quota for this site
                                      has been exceeded.";
 reasons[G_GEO_SERVER_ERROR]       = "Server error: The geocoding request could not be
                                      successfully processed.";
and display the text associated with the reply.Status.code.

When using geocoder.getLocations(), accessing the status code is straight forward, see this example

When using geocoder.getLatLng(), the status code is not returned. You could follow a failed getLatLng() with a getLocations() request and examine its status code. There is a possibility that the status code might be different, in particular, if there was a server timeout on the first attempt, the second attempt might even succeed.

I recommend avoiding geocoder.getLatLng(). It might seem to make the coding easier, but the lack of error handling makes things more difficult in the long run.

Fitting the zoom

The geocoder now returns an ExtendedData section which gives details of a Lat/Lon box that can be used to zoom the map appropriately. Here's an example.

In that example, if you search for "France" you get zoom level 6. If you search for "123 Avenue des Champs-Elysees, Paris, France" you get zoom level 16.

Note that the Lat/Lng box isn't a perfect fit for the target location. It's just there to provide sensible zooming.

Potential Pitfalls

  1. Be aware that geocoder requests are asyncrhonous. The request is sent to the geocoder and processing continues immediately without waiting for the reply to come back.

    Make sure that all the code that operates on the results is placed inside the event handler function.

  2. Don't send lots of requests at once. There's a rate limit on the number of geocode requests that you can send per second.

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