问题
There are some free databases on the internet. But it's interesting to know, in what way they are formed. Can you suggest some?
回答1:
MaxMind has a good description:
The idea behind GeoIP is simple but the process is complex. We employ user-entered location data from sites that ask web visitors to provide their geographic location. We then run millions of these datasets through a series of algorithms that identify, extract, and extrapolate location points for IP addresses.
回答2:
There isn't a formula to convert IP address to geographic location. You get some clue through whom the IP address is registered to. That isn't perfect, though. A block of addresses belonging to Google or HP may not tell you much since they are spread over many locations. Looking at the network path to reach an address (routers along the way) gives some more clues. Most geolocation databases are compiled in this fashion - using known information about neighboring IP addresses and making a best guess. Some providers will solicit information by asking you to correct their best guess of where your IP address is located.
来源：https://stackoverflow.com/questions/1884099/ip-location-database