Behind every Google Map, there is a much more complex map that’s the key to your queries but hidden from your view. The deep map contains the logic of places: their no-left-turns and freeway on-ramps, speed limits and traf c conditions. This is the data that you’re drawing from when you ask Google to navigate you from point A to point B – and last week, Google showed me the internal map and demonstrated how it was built. It’s the rst time the company has let anyone watch how the project it calls GT, or “Ground Truth,” actually works.