BBC:

Cab drivers' grey matter enlarges and adapts to help them store a detailed mental map of the city, according to research.
Taxi drivers given brain scans by scientists at University College London had a larger hippocampus compared with other people. This is a part of the brain associated with navigation in birds and animals.

The scientists also found part of the hippocampus grew larger as the taxi drivers spent more time in the job.

Though the story is very old (2000), it's worth reconsidering because it's about a kind of city and brain that's pre-GPS (or before the true commodification of GPS). This product is currently transforming the city. Your brain doesn't need a sophisticated mental map to navigate urban space. The city is demanding less and less brain space. This demand or pressure will finally disappear, vanish into the ether of cyberspace. We will no longer remember the city in the way we no longer remember phone numbers. What kind of brain will we need?