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When using the HTML5 geolocation API I get, apart from latitude and longitude, also the "accuracy of the location in meters". What exactly does that mean (meters is not a unit of accuracy)?
I assume it shall be read as "with probability p the request was made within a meters of the returned location" - if so, what is p? Is it one standard deviation (p = 0.682?) Two standard deviations (p = 0.956?)
http://dev.w3.org/geo/api/spec-source.html isn't really explicit either.
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Accuracy refers to the degree of closeness of the indicated readings to the actual position. The accuracy of GPS results depends on a number of factors: Number of channels on the receiver.
Depending on the availability of GPS on the device and the quality of the mobile/WIFI signals, HTML5 geolocation can be very accurate i.e. to a street level. Hence it can be used to pin point a device's location making it a very useful technology for websites or apps that require the exact user's location to work.
It has the highest accuracy; in most Android smartphones, the accuracy can be up to 10 metres. Mobile phone tracking is used if a cellphone or wireless modem is used without a GPS chip built in.
Geolocation sources Mobile devices tend to use triangulation techniques such as GPS (accurate to 10m and only works outside), WiFi and GSM / CDMA cell IDs (accurate to 1000m).
Quoting from the spec:
The accuracy and altitudeAccuracy values returned by an implementation should correspond to a 95% confidence level.
So, 95% confidence level it is. Then again, implementations can vary significantly in what they report...
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