They're almost certainly using barometer data from Android devices to help know elevations and differences between roads. The barometers can measure altitude differences as small as ~0.5m - it's pretty amazing.
That's interesting. What kind of datastream do you get from that sensor? Something that has a useful ∆Z over short intervals but essentially no absolute accuracy?
You can check it out yourself if you like - I provide a live feed of barometric data from Android sensors at http://pressurenet.io/. The data I collect is polled every 10 minutes, and while the exact pressure is often nearly useless due to noise, trends in the data are very clear. I'm looking specifically at the weather, so over periods of ~6 hours we get really really clear trend lines.
When a device moves rapidly in a short period of time, you know that the sensor data will be reflecting the altitude changes and not the weather changes. Moving the device from my feet to my head shows a clear change of ~.5mb typically.
