GPS is great, but it isn't always accurate. It's susceptible to interference, especially in urban settings, which is why Boeing is working on a new system to fill the holes that GPS has when it's really needed.
The objective of the Robust Surface Navigation (RSN) program is to develop technologies that can exploit various "signals of opportunity"—electronic waves emanating from satellites, cellphone towers and even television transmission towers—to provide precise location and navigation information to ground troops when GPS signals are being electronically jammed or blocked by natural or man-made obstacles, such as foliage or buildings.
Sounds pretty cool, but don't get excited for the navigation to improve in your Escalade anytime soon — this is being developed first and foremost for the military, and it won't be ready for their use for years. Patience, my pets.