A lot of apps need to map IP addresses to locations. Jeremy Cole in
On efficiently geo-referencing IPs with MaxMind GeoIP and MySQL GIS succinctly explains the many uses for such a feature:
Geo-referencing IPs is, in a nutshell, converting an IP address, perhaps from an incoming web visitor, a log file, a data file, or some other place, into the name of some entity owning that IP address. There are a lot of reasons you may want to geo-reference IP addresses to country, city, etc., such as in simple ad targeting systems, geographic load balancing, web analytics, and many more applications.
This is difficult to do efficiently, at least it gives me a bit of brain freeze. In the same post Jeremy nicely explains where to get the geo-rereferncing data, how to load data, and the performance of different approaches for IP address searching. It's a great practical introduction to the subject.
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