This TEDx Dublin talk from Aris Venetikidis is pretty fascinating, especially to the design geeks out there. In the talk, he covers how the maps we build in our heads are usually pretty wildly different than the actuality of the terrain, simplifying streets to be straight, turns to be 90° or 45°, and attaching emotional importance to locations along the way.
Developing maps that actually work, especially public transportation maps, requires an understanding of how our brains process our location. Public transportation maps are especially reliant on this, since they can be complex yet their relationship with the actual topography of the city is less important. That realization is what led Harry Beck to radically change public transportation mapping when he designed the London Underground map like a schematic diagram as opposed to a cartographer's map back in 1932.
Venetikidis uses Beck's work as an inspiration as he seeks to redesign the map for Dublin's insanely complex center-city bus system. These are interesting problems with interesting solutions, and as drivers I'm sure we all have very idiosyncratic maps of our cities in our heads.
I'd kind of like to see everyone's head-map, now that I think about it.
(Thanks, Leo Kent!)