Ever wondered how sites like Google and Yahoo! always seem to know which country you're in, and automatically redirect you to the most appropriate country sub-site? Or how some Web sites display advertisements perfectly targeted to your city or region? Well, it isn't magic -- these sites are simply mapping your IP address to a geographical database to identify your location, and then using this information to send you precisely-targeted data.
They work through the steps to get it up and working - the installation, a few basic code examples to show how to use it, and a full example of how to target different areas with different kinds of ads (geographically-targeted advertising).