GPS is virtually synonymous with navigation, but GPS exists at the whim of the US government, so shouldn't I be concerned? The answer is that I am somewhat concerned, but that I also do my part in trying to reduce our dependence on that system.
I'll venture to bet that everyone reading this knows what GPS is, but I suspect fewer people realize that GPS is entirely owned and controlled by the US Department of Defense. In other words, the millions of GPS enabled devices work because the US government allows them to work, and if the US decided to shut the system down, even temporarily, it could mean disaster. Am I worried? Not really.
Disabling GPS Would be a Financial Disaster
The GPS system is used worldwide, in everything from airplanes to cell phones. If that system was degraded sufficiently, or shut down even temporarily, it would cause a global financial disaster.
Even if the US were to only select certain satellites and to degrade the signal over certain regions, there would likely be unforeseen consequences which would eventually effect the US financially.
In addition to any immediate consequences, there would also be long term issues raised around US reliance, which is a topic of increasing concern internationally, especially after recent NSA revelations.
GPS is Not the Only Game in Town
Even if the US were to shut down its system, the US's GPS system is not the only satellite navigation system. Russia's GLONASS system, China's Beidou system, and Europe's upcoming Galileo system are all offering services which are similar in functionality and quality to GPS, and with all in one chips coming out, there will be even less incentive to degrade any one system's service.
Ground Based Location Systems Exist
In addition to satellite navigation systems, we can, and often do use ground based navigation systems. Airplanes use a variety of land-based augmentation systems such as WAAS and cell phones can determine their location by use of cell tower triangulation.
In addition to these methods, by looking at other signals, such as Wifi access points, one can lookup their location. Both Google and Apple use a combination of cell tower data and wifi access points in augmenting their GPS systems.
The Mozilla Location Service
There have been a number of cell and wifi collection services. All of them have so far been either technically lacking or proprietary in nature. That's hopefully changing with the Mozilla Location Service, a new Mozilla project to provide an alternative to the popular proprietary services, including source code to both the server and client and, once the privacy issues are sorted out, a downloadable database of locations.
My personal contribution to the project is that I run their data collection client, MozStumber on my Android phone, and I encourage others to do the same.
A Free GPS Service?
Would it be better if we had our own navigation system owned by the community, used as a common resource in the same way that Free/Open Source software, and the OpenStreetMap project serve the community. Of course it would, but do to that, we'd need millions of dollars in development, construction, launch and maintenance of the satellites needed for the effort. Even with advanced in amateur rocketry and satellites, I don't think that this project will be feasible in the near future, but it's also not necessary with so many existing alternatives.
So don't worry about knowing where you are, you're covered.