Turn an address into a region with Google Maps Api

I want to create a website that allows the user to enter in their address and get back their local representatives in Ireland.

So the way I see this working is that I use some google tool to开发者_开发知识库 define what the regions (electoral constituencies) are in Ireland and then when a user enters their address google returns which region they are located in.

Can anyone explain how I would do that?

---

Found the solution here: http://appdelegateinc.com/blog/2010/05/16/point-in-polygon-checking/

And an implementation is here: http://www.politicswiki.ie/Special:ConstituencyFinder

Check out the license if you want to reuse