At the risk of both taking a cheap shot and perpetuating an industry stereotype, I haven't encountered too many geographically genius-level taxi drivers in my city.
I'm just happy if they have a GPS navigation system and can vaguely understand the directions issued from same.
You probably don't live in London, then:
http://en.wikipedia.org/wiki/Taxicabs_of_the_United_Kingdom#...
When taxi drivers are required to demonstrate a deep knowledge of the geography of their area and are not allowed to rely on maps or GPS navigation systems in order to be certified, you end up with taxi drivers that are very good at navigating the city.
Another case in point: taxi drivers apparently have growing brain regions for geographic stuff (learning their city by heart). I guess you wouldn't expect most taxi drivers to have above average intelligence, but if you tested their geographic "senses", they might register as geniuses. But they also probably didn't become taxi drivers because of their talent - it developed by them being taxi drivers.