/maps/community?hl=en
/maps/community?hl=en
6/14/18
Original Poster
Flash

Location Accuracy

Hello,


A very frequent question on the forum is regards to location accuracy, including how it relates to Location Sharing and your Timeline.  If your post has been duplicated to this post it is because this post will provide the best answer we can offer.


A phone uses various methods to interpret its location.  GPS is the most exact, but lacking a GPS signal your phone can rely on triangulation between cell phone towers and/or the previously recorded locations of wifi that it can see.  Triangulation has error involved, and using wifi can quickly be defeated if a wifi router has been relocated since it’s position was noted, which can cause phones near it to think they are several to hundreds of miles away from their actual position.


GPS can also have issues.  An fairly accurate GPS location requires a line of sight to at least 4 GPS satellites which need to be widely separated.  Once you are among tall buildings, under tree cover, or indoors issues can be encountered with reflection of signals and with the satellites being used to being spread apart enough.  If the signals from various satellites bounce off of walls, buildings, etc. multiple times before reaching your phone then the amount of time for them to get from the satellites to your phone is increased.  The amount of time it takes to get to your phone is what is used to calculate how far you are from each satellite, so reflecting signals cause error while still making your phone think that GPS is available and thus the best location method to use.


Most people do not realize that being indoors causes such inaccuracies because your phone is automatically error correcting.  As an example, please look at the below GPS track from a GPS logger that is much more precise than the average phone GPS but which has no error correction occuring.  This track was recorded indoors, but near very large windows that minimized the inaccuracies introduced. During the recording the logger did not move at all.



When looked at live the GPS position can actually be seen to be constantly in motion, wavering around your actual position.  This effect is known as GPS drift. When indoors GPS drift can be much worse. Your phone has error correction that realizes that this is likely drift and automatically holds the position still for most of the time.  When there is a sudden position change such as the one to the north the error correction will likely ignore it as drift if it only occurs for a second or two, but any longer and it will assume you have moved and will report the new location.  Due to the error correction that has been occuring this would not show as you moving, but rather the phone would suddenly report a large position change. The large drift to the northeast is more prolonged and almost certainly would have a phone report itself as repositioned even though no actual repositioning occured.


Keep in mind this track was recorded over a brief period on a device more precise than the average phone GPS.  If this was instead on the less precise GPS in a phone, if it was over a longer period (or over many days), and if it was further indoors with more normal sized windows then we might see a lot more errors manifesting themselves as sudden position shifts to other locations, with some of them being much further away.


Errors are also going to vary from phone to phone, both due to different hardware and different error correction.


GPS errors, triangulation inaccuracy, and the uncertainty of using surrounding wifi can all make your phone misreport you location at any time.  This then can also cause your Timeline to record inaccurate data, and for your phone to report an inaccurate location to Location Sharing.


Additionally, sometimes Location Sharing only updates once or twice an hour or less, especially if it thinks it’s not moving; so if your phone reports the wrong position for just a minute it still might show up as a long period at that location on someone else’s phone when it doesn’t update after.


And finally, if you have ever looked over the Timeline feature of Maps you will find that Maps assumes that when your phone reports you has being in one area for a time period then the assumption is made that you were at the closest feature on the map, further adding error while also making it seem like you were at a precise location.


I personally have seen my wife’s position being reported a long distance away from where I know her to be, which is sometimes right beside me!  She has seen me as having gone to Costco when I didn’t get within 3 kilometres of it. I also just yesterday drove almost 80 kilometres away from my office, but on the desktop version of Google Maps my blue dot “phone position” showed as still being at the office.


In summary, both Location Sharing and Timeline are handy features that are fairly reliable, but they are not infallible and do provide inaccurate results on occasion.  No one should rely on it as a guarantee of the location of a person, as one’s phone can and will report its location inaccurately.


For those wanting to know more about GPS inaccuracies a good primer can be found at https://wiki.openstreetmap.org/wiki/Accuracy_of_GPS_data.


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All Replies (3)
True Licht
7/14/18
True Licht
Flash,

Very helpful.  Hope you have better luck keeping track of your wife.  I have no idea where my wife is most of the time.

We track a delivery truck with Google Timeline.  When using "Your timeline" I usually display "Raw Data" from the little gear-icon in the bottom-right-corner of the Google Map.  Looking at the individual raw-data-dots it seems clear to me that our AT&T Android smartphone is uploading their location to Google at exact 5-minute intervals (if the truck/car is moving).  If our smart phone pinged Google every 1-minute instead of every 5-minutes I think the maps would be more accurate.

7/14/18
Original Poster
Flash
It would be more accurate, but it would also use 5x the battery.

The GPS logger I used to produce the above blue track records once a second.  I have it to use to geolocate photos I take with my SLR, I've been doing so long before smart phones.  There are multiple apps that will do the same, but they will also quickly kill the battery.  But if you need such a level of precision and if you have the phones hardwired in so that battery is not a concern, there are such solutions out there that will "phone home" as often as you want.
True Licht
7/14/18
True Licht

Flash,

 

Good points.

 

Looking at settings/battery and settings/cellular we see very little battery or cell-data being used by Google Maps Timeline.  The big users are Safari, Mail, Messages and Home&Lock Screen.  We were surprised at how little data Google Maps Timeline was using.

 

The problem is that a truck can move a fair distance in 5 minutes and the resulting Timeline maps are very inaccurate.  But, at least you get a fair idea off where the major loading and unloading stops were and how long those took.  Short stops here and there are missed.

 

If Google would let you change the ping-time from 5 minutes to 1 minute it would be great.  With a 1-minute ping all of the quick-stops would be recorded.

 

Of course this conversation came-up because thousands of people are always asking every day why Google Maps Timeline is so inaccurate and the resulting answers are incorrect.  The primary reason Google Maps Timeline is inaccurate is because the ping-time is 5-minutes.  All the other answers discussed obfuscate the situation, making it more confusing and perpetuates a situation of no one understanding the problem and solutions never being developed.

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