Possible Duplicate:
Location detecting techniques for IP addresses
For our website it's important to know from exactly which country our visitor is coming from.
I guess the best answer for my question would be the simple geo location feature of current browser systems, which just ask the user if the website is allowed to see his geographic location: http://dev.w3.org/geo/api/spec-source.html
but I don't want to bother visitor with questions, I would love to automatically detects the visitor's location (country should be enough.)
What's the best way to do this? - what ip database would be the best? - is the browser header trustable enough to detect his country? (en-us en-en en-ca?) What's the best solution?
NetImpact provide a free API for geolocation lookup by IP, ProgrammableWeb also has a roundup of GeoIP lookup providers. This involves a small amount of latency while your application completes an API call (unless your application can use a non-blocking call) but is the least intrusive manner of detecting a visitor's country of origin.
The browser header just tells you what language the user wants to see. A Spanish-speaking person on a business trip to Japan probably wants to see websites in Spanish.
I think you can use reverse-IP services to make a guess, but if it's for commerce purposes I think you have to ask the user to tell you.
Similarly with geo-location: the physical position of the computer may or may not be relevant to the needs of the user browsing the site.
Have a look at this page on the Google Maps API: http://code.google.com/apis/maps/documentation/javascript/basics.html#DetectingUserLocation
http://www.iplocationtools.com/samples.html also presents a good set of apis to do this. I have used their system before and they were quite reliable.
来源：https://stackoverflow.com/questions/4179000/how-to-detect-country-location-of-visitor