It's wonderful to deal with keywords that have 5,000 searches a day, or even 500 searches a day, but in reality, these popular search terms actually make up less than 30% of the searches performed on the web. The remaining 70% lie in what's called the "long tail" of search. The long tail contains hundreds of millions of unique searches that might be conducted a few times in any given day, but, when taken together, comprise the majority of the world's search volume.
Now the ad servers don’t create this table themselves, they license it from another company like MaxMind or DigitalEnvoy, whose primary business is geolocation data. This is no enviable task; IP addresses themselves don’t necessarily have an obvious pattern in the way they are assigned like a telephone area code would. It’s a bit like solving a mystery, and the geolocation companies use a variety of methods to approach the problem. /injects>