Comment 33 for bug 892370

The tzdata mailing list pointed me to the Mac implementation. I don't know if they managed to avoid the problem of cities being too close in a 10x10px area. They are using geonames as well, and the smallest city data-set is cities where population > 15000, which we're already using.

http://uiobservatory.com/2010/what-time-is-your-zone/