I have again found a nice article about how to match IPs to countries over at builder.com. It uses PHP::Pear's Net_GeoIP class for the querying. But what really interest me is the data behind it. Luckily MaxMind does provide this data in various flavors.

There is a free CSV export at the beginning of every month, which can be downloaded on country level and on city level.

However there are also 2 APIs for PHP. For once there is a pure PHP implementation and also a PHP extension as well.

I am definately going to try these out!