It’s been 20 years since the U.S. Air Force did the world a solid by granting full access to the Global Positioning System. In that time, motorists have moved from crude, monochrome line maps to 3-D topographic displays rendered with skies, buildings, and live traffic information. But even after the Defense Department agreed to stop scrambling civilian signals in 2000, GPS isn’t accurate enough for the next generation of drivers who won’t drive their cars at all. And all those assists that allow hands-free operation for a few amusing seconds also could use better information.

High-definition mapping is the core of tomorrow’s autonomous cars. Radar, LIDAR, and visual cameras are only feelers to a car’s immediate vicinity. Picture an ant crawling through grass, navigating blade by blade. HD maps would render every last strand of the entire lawn—and locate that hard, black surface where those giant wheeled death machines prey on tiny insects. Whereas a regular map can position a car’s location to within a meter, HD maps can do it to within as few as 10 centimeters. It’s why Audi, BMW, and Daimler purchased a Nokia spinoff, called Here, for $3.1 billion in August. The deal grants them navigation software to power their next autonomous prototypes and, once the lawyers sort it out, the real things.

“It started from us looking at how to move from representing the standard navigation map to how you present reality in 3-D,” said Here senior engineering director Vladimir Zhukov. “You need another order of magnitude in the precision.”