As the designated late friend who takes hours to get dressed and is always fashionably behind schedule, I mentally rely on Google Maps' ETA. Instead of, you know, actually leaving for my destination, I almost always sit there wondering: how does Google Maps know that traffic is there before anyone's had the chance to report it? When you first install Google Maps, the very first thing you're asked to do is give it access to your location. The moment you grant Google Maps this permission, you become of the millions of sensors feeding the whole system. Every time you drive with Google Maps open and your location enabled, your phone sends anonymous bits of data back to Google describing how fast you're moving.