Commercial, non-military GPS is only accurate to about 7 meters or so, and that number is currently capped by the US administrators of the service. How do you propose that they make it more accurate than that?
This information is 15 years old. USA turned off Selective Availability on May 2, 2000 and GPS has been available with sub-meter accuracy to civilians ever since. See
www.gps.gov/systems/gps/modernization/sa/
Also, most modern smartphones made in the last 2 years now runs on multiple GNSS simultaneously, not just GPS. The latest Android, iPhones and iPads lock to
both GPS and GLONASS simultaneously for a more accurate lock, and I observe I am almost always easily able to tell which lane I am on the freeway, when I'm running a GPS app in non-snap-to-road mode (e.g. Google Maps with GPS navigation turned off), as long as I'm driving under open sky. Even urban canyons (Toronto downtown) have recently become pretty accurate on new smartphones, my GPS lock has stopped jumping around. Some
Qualcomm chips built into cellphones today now have support for GPS (USA), GLONASS (Russia), BEIDOU (China), and GALILEO (Europe) and is capable of syncing to all of them simultaneously for an even faster or more accurate lock. If you have an iPhone 5+ or an iPad Mini Retina LTE, you're already using Russia's GLONASS simultaneously with USA GPS when you use Apple Maps. Speed of GPS lock of a high-end Galaxy or iPhone is more accurate than a typical cheap/old Garmin unit, and also lock much faster (<1-2 seconds) thanks to ephmerisis (an almanac that tell the phone how to find the satellites) downloaded over LTE airwaves rather than waiting 30 seconds to sync to the satellites. Also, what we call "GPS" in smartphones today isn't just GPS only anymore, it's now listening any location satellites in the sky of all the supported locator satellites (including other countries'). Over
100 smartphones already support Russia's GLONASS, even when you're using it in USA or Canada.
Frequently, I've noticed my iPad Mini Retina locates at sub-meter accuracy today, if I'm outdoors in an open area. In "Find My iPhone" (of which both an iPhone LTE and iPad LTE is set up on, in case I lose the other), it correctly told me which side of which car I forgot my iPad LTE in, in the middle of a parking lot, right down to the correct side of a specific car (left side or right side). The lock is not always that accurate, but situations of sub-meter location lock is becoming more and more common on consumer devices, even during times when there's still a 3 meter blue "error margin" circle, but the center dot is exactly where it is (down to ~0.5m).
The bottom line is smartphone navigation (e.g. Google Maps, Apple Maps, etc) on modern devices made in the last two years will continue working fine even if USA shuts down GPS completely....because it's also locking to the GLONASS satellites (and increasingly BEIDOU / GALILEO as the count of their satellites increase). And ironically, Russia's GLONASS is reputedly more accurate than GPS. No single country has control anymore over degrading mapping precision of your phones anymore! It will only get better when the BEIDOU / GALILEO constellations are completed.
Apologies for the topic diversion, but it amazes me how little people know about satellite location services except for erratic behavior of bargain-bin GPS units or in old phones.
