Address Validation Using Google Maps API

Answer :

The answer probably depends how critical it is for you to receive support and possible customization for this service.

Google can certainly do this. Look into their XML and Geocoding API's. You should be able to craft an XML message asking Google to return Map coordinates for a given address. If the address is not found (invalid), you will receive an appropriate response. Here's a useful page: http://code.google.com/apis/maps/documentation/services.html#XML_Requests

Note that Google's aim in providing the Maps API is to plot addresses on actual maps. While you can certainly use the data for other purposes, you are at the mercy of Google should one of their maps not exactly correspond to your legal or commercial address validation needs. If you paid for one of the services you mentioned, you would likely be able to receive support should certain addresses not resolve the way you expect them to.

In other words, you get what you pay for ;) . If you have the time, though, why not try implementing a Google-based solution then going from there? The API looks pretty slick, and it's free, after all.

Google's geocoding api does what want you want. As Xerus points out, as long as you are not using the geocoded points on a non-google Map, you should be good (terms of service). Specifically,

3.1 Use without a Google Map. Customer may use Google Maps Content from the Geocoding API in Customer Applications without a corresponding Google Map.   3.3 No use with a non-Google map.  Customer must not use Google Maps Content from the Geocoding API in conjunction with a non-Google map. 

I am both a web developer and a former employee of one of the companies you mentioned. I completely understand where you're coming from. Verifying addresses seems like a simple problem to tackle, but it's very much an iceberg. I suppose one workaround to the legal constraints of the Google or Yahoo! Maps APIs is to request your users verify their addresses on a map. If I were in your shoes, though, I wouldn't go that route.

The reason address verification services are so expensive is that they require licenses and ongoing relationships with grumpy, bureaucratic postal authorities (including the Royal Mail). Unfortunately, postal authorities are the best (and often the only) sources of data against which to verify addresses, so there really isn't any other way to go about it. The bottom line is you need to weigh the cost of bad addresses (usually a question of mail volume) against the cost of the software to verify them. Irish postal data is even more rubbish than Irish postal formats (which frequently omit building numbers), so there's little you can do about those addresses.