Localisation

Hi, I would like users of my Website to be able to select the country they are
in and if they want to their local district or county. The content of the web
site will then reflect this selction.

I would like advice on how to implement these selectable countries and
regions and where I can find the country and district data for this. Once I
know how to tackle this, I'll look at how to use a database and SQL statements
to display the relevant data.

Many Thanks, Paul