And this is why you are an "Honorary PhD" on here! Very interesting information. I see how the original use was military use so understand how the government backs the infrastructure. Here is one thing I am willing to contribute some tax dollars to.
Ben,
Back from GPS start in the 1970's the military used "selective availability" to reduce the accuracy of the GPS signal available to non-military receivers, instead of being as little as 1 meter from your absolute global position, you could be as much as a 50 meters horizontally off to 150 meters vertically off, so was of little use as an enemy missile guidance system, but also of limited use for aircraft . It also made commercially available units not effective for wartime use, and selective availability was turned off for a while during the Gulf War.
May of 2000, President Clinton removed the selective availability, and the FAA was able to not have to rely on their own system of location so much, reducing costs maintaining stations far away from airports.
As a historical tidbit, LORAN continued to be preferable to many fishermen over GPS in the early days. Even with selective availability randomly creating location inaccuracies, it was far more accurate overall than LORAN, but LORAN could precisely return you to a little outcropping of coral or some other invisible feature that would be difficult to pinpoint with GPS and a paper chart.
Recently purchased a Garmin Oregon 600 GPS loaded with complete street maps of Canada, USA and Mexico. My first GPS units from the mid-1980's and early 1990s just showed Latitude and Longitude, requiring buying paper Lat/Long maps or charts of every location you wanted to sail to or visit with accuracy- and those paper maps were only as accurate as the cartographers could measure bit by bit, and one's own lining up on the cross-hairs.
I probably have recycled 25 pounds of paper maps and charts that cost hundreds of dollars, though still have quite a few- never know when a big EMP might knock out the GPS ;^).
Cheers,
Art
