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.

As of late 2014[0], Google engineers admitted the mapping required for their cars to work wasn't feasible at a nationwide scale, and that if they didn't know to look for say, a stoplight, on their maps, they'd run right through it. (Looking for arbitrary red lights is probably a hard problem too.)

That's two years ago, yes, but they've announced nothing, technologically, in this field in this time (please comment if you have an additional source relating to the mapping of the roadway for a Google car), despite tons of PR about the number of miles they've driven or what cities they were driving in, with the same technology they've already had. Also bear in mind, almost all of Google's senior talent in self-driving cars has left Google X. So if they were having trouble with this problem in 2014, their newer, less experienced people now, probably are having more difficulty in 2016.

[0]http://www.slate.com/articles/technology/technology/2014/10/...