There was a recent Japan's Top Inventions episode on this:
https://www3.nhk.or.jp/nhkworld/en/ondemand/video/2091030/
It's very much the same content, but in video form.
Summary: current location of car is tracked using dead reckoning[1], then plotted against maps that were printed on transparencies. Highlights include using the rocket-inspired gas-rate gyro for finding car heading, and figuring out that the car's location tracking was more accurate than the maps they were testing with.