If I'm not mistaken, this is the presentation that discusses mapping the roads before autonomous travel. They compare the maps to what the car sees as it drives. https://www.youtube.com/watch?v=YXylqtEQ0tk

But there are a number of reasons the need pre-mapping are not a huge issue. A) When autonomous cars start to be introduced people will still know how to drive, and can pilot the car through unmapped areas. By the time everyone has an autonomous car, and no one knows how to drive the world will be mapped. B) Google has already shown with Streetview that they can create detailed, up-to-date maps of most roads. C) This problem will likely be solved in time.