So if I wanted a GPS service to locate a very specific spot within, say, ten feet, is that something current phone tech would be capable of?
Without WAAS or differential GPS the civilian form of GPS has an accuracy of 4 meters RMS or around 7.8 meters 95% of the time in theory but ends up being around 15 meters in reality.
The main limiter outside of cost for a cell phone will be size, cost and power conserns.
Equipment use for surveying will often use multiple sources like GPS, GLONASS, and Galileo and ground based corrections like WAAS and the phase angle of the radio waves to get the error within a centimeter.
The limitations on phones are due to product requirements like I mentioned above and not limitations of what is practical with the signals themselves.
Thanks! What do you think are the limits of accuracy on phone GPS systems? Is it a matter of waiting for tech to catch up with potential?
My iPhone 6 will put me in the correct room of my house.
The primary limiters are probably that consumers prefer to buy inexpensive small phones with a long battery life over a larger, more expensive device with less battery life that is more accurate.
Remember Apple removed the headphone jack to reduce the device thickness; so even if the above statement applies to what manufactures think consumers want it directly relates to what products are on the market.
As new receiver chips add in features and reduce power requirements it will improve a bit but I doubt the accuracy will ever be state of the art in phones. The number of consumers who need that level of accuracy is just not a significant portion of the market today.
Rat avatar, thanks for the information! OK, so if, say, a company provided a service which involved using a GPS to locate something - think of it like a modern version of the proverbial map to buried treasure - and customers wouldn’t need an app or a high-end phone, but were provided with the high-end hardware on-site…? Feasible? Or am I asking for too much, too soon, from our current tech?
Not a problem, those products exist.
You could do this with a normal smartphone GPS receiver, by recording a whole bunch of positions over time, and averaging them.
General population GPS accuracy is limited by several things not the least of which is the government which releases the data. Here’s a write up I did for a geocaching site:
… that includes other causes. The accuracy of the device is only a small part of the issue.
With out knowing what you are trying to achieve, I’ll also offer this solution: https://what3words.com
If you had GPS coordinates where X marked the spot somewhere in a park, you could plug those coordinates into your phone and start walking around. Your phone GPS would ‘Ping!’ when it thought it was at the right spot. However, due to inherent inaccuracies it would ping right across an area of maybe the size of a tennis court. Going back and forth you might find it narrows down to a smaller area - say a swimming pool, but either way you have a lot of digging ahead of you.
Alternately, you hire a land survey firm with a high-end GPS unit. They will be able to get the location down to a metre or, if the original location specified accuracy down to millimetres, then probably get it so close as to not matter.
Your phone app will be designed to be usable by the novice, a hand-held GPS will be more accurate but you’ll need to definitely read the manual and play with it first, and the high-end unit will require an experienced operator.
Thanks so much for the replies! What I’m getting at is something like, “OK, let’s say I need to tag and later locate something like the site of an in situ fossil that I need to revisit later”, or “I have a pet turtle that wanders off, can I tag him somehow so I can find him when he goes wandering?”
For the first, read your phone’s GPS location, and put a Bluetooth low energy beacon right where the fossil is. For the second, just tape the beacon to his back (the poor thing).
These beacons are sold as key finders or location tags or something along the lines.
That won’t help him to know where he is, only to remember where his phone thinks he is.
People do this all the time - it’s called geocaching.
Generally, a phone is more than accurate enough to get you where you want to be.
Yes, but one of the many things the OP offered is something about a treasure map. The OP could get a better answer if he wasn’t so coy about exactly what he is trying to achieve.
Based on my phone’s running app, I would say 10 feet isn’t going to be a reliable result. It mapped my mile at dozens of locations on the exact same route and the farthest were 50 feet apart.
I read that mountain guides use phones’ GPS to navigate on tricky trails and I think that’s horrifying!!
Oh, and there’s another way to increase your GPS accuracy - use the mapping app on your phone.
Let it determine your location using GPS, then zoom in and note your position relative to visual landmarks, and drop a pin where you think you really are. Probably get within a few feet with that.
If the OP is planning to hide money or valuables by burying it, all he’d need to do is record both the GPS coordinates and bring a tape measure along. Choosing some unlikely to change landmarks - specific large trees, large rocks, the corner of a property line - record the distance from each of those landmarks. Record some redundant ones - maybe 5 or so - so that if one of the landmarks is removed or destroyed over time, you could still get the exact location using the measurements from the remaining landmarks.
The OP could also alleviate his worried about cell phone accuracy by using a second phone of a different make/model. If the 2 phones give very closely agreeing coordinates to the same spot, the measurements are likely correct in absolute sense. The OP could also check on Google maps the lat/long to that spot - just make sure he does it in incognito mode/clears his browser history 
I think its clearly a golden turtle, there are just too many clues the OP has dropped.
Yes, by all means measure from fixed landmarks. Also if your secret burial site is blessed with decent views of scenery, or humanly made objects, just take some photos with your phone. Its usually easy enough to work out exactly where you were standing when you took them.
For navigation, 10-20 feet is plenty. It’s more for bushwacking than “tricky trails” which for the most part just means poorly marked.