There is at least one community database to take the network (IP) address that web requests are coming from and make an educated guess about geographic location. This is how web searches and weather queries can return localized information.
Google has a nifty feature by which they use such a geolocation database and project visitor counts onto a map of the world. The map on the left, for example, was created from last month's visitors to this blog. The big circle in the center of the US corresponds to Norman, which (as expected) has the greatest concentration of readers of this blog. The world-wide extent of my readership is a sampling artifact: over the last month, the two most visited posts were on Tata Jaguar and on Google Android -- I would venture that if I were to filter those two posts out, the map would be far more concentrated, and make much more sense.