I know the security-minded among you are going to start complaining that it would be easy to add a nonce, but we'd rather avoid that. Our strategy is to serve virtually everything from cache.

[1] http://wiki.nginx.org/HttpGeoIPModule

All user request have an X-AppEngine-Country header which contains the ISO-3166-1 alpha-2 country code for the user, based on the IP address of the client request.

(from Version 1.5.1 http://code.google.com/p/googleappengine/wiki/SdkReleaseNote...)

    Geo = { /* object literal */ }

    <script src="http://geoiplookup.wikimedia.org/"></script>
    <script>geoloaded()</script>
    </body></html>

    <script type="text/javascript">
        var response = undefined;
    </script>
    <script type="text/javascript" src="...">
       // response = { .... };
    </script>
    <script type="text/javascript">
       _callbacks[1234](response); // response == undefined means error
       response = undefined;       // allow garbage collection
    </script>
    

http://www.maxmind.com/app/geolitecity

http://www.geoplugin.net/json.gp

Other formats here: http://www.geoplugin.com/webservices

Have been using it in production now for several months, works great.

https://github.com/krickert/IPAddressZipCodeStateCountryLuce...

It downloads one of the many free DBs of IP addys and makes it into an index. You can do geo spatial searching APIs with IP addys.. Fun stuff.

It's a sinatra app which uses the MaxMind data, typically responds in < 1ms, and it has caching built in (if you deploy it to heroku).

I find it strange that depending on the device, that I will be detected in different areas (even within the same service).

For example: Google Maps says I'm at a park about a 10 minute drive from my current location. But if I view the mobile version of it on my iPod, it can find me to the room of the building I am in.

Anything that's not google or apple puts me in Hamanako, which is a 2 hour drive on the expressway.

I can't seem to find the relevant mailing list threads, but here's some evidence of ad-hoc accuracy testing last August: http://meta.wikimedia.org/wiki/MaxMindCityTesting