London taxi drivers must learn all 25,000 streets and some 100,000 landmarks within a six-mile radius around Charing Cross, as indicated by the black circle. As they learn and practice their profession, London cabbies don’t just fill their brain with knowledge — the knowledge literally changes their brain. A 2021 study shows how trainee cabbies learn by layering streets like a living GIS system, turning abstract geography into visceral knowledge. Another study made a useful distinction between taxi drivers and bus drivers. Recent research suggests that taxi drivers (and ambulance drivers) have some of the lowest mortality rates due to Alzheimer’s.