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Comment by barbazoo | Hacker News Reader

Does anyone know what Maps actually uses Wifi for? I read it's to increase accuracy but is it really that common that GPS accuracy isn't precise enough? I get that there are GPS blindspots e.g. tunnels, downtown "canyons" but Maps is pretty smart at interpolating one's location by using accelerometer data.

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Getting a GPS fix from scratch (aka a cold start, where the receiver doesn't know anything in advance) takes minutes.

Even if you take advantage of tricks like out-of-band time, almanac, and ephemeris data, it can still take in the neighborhood of 10 seconds to get a fix. I imagine wifi is also less susceptible to issues that plague GPS like multipath and urban canyons

It is exactly that. Increased accuracy. Think of driving on a tight street, buildings left and right and buildings with 10-15 floors. It will take forever for the GPS to get "enough" to be able to give you an accurate reading fast. But if 20 cars have passed in various speeds, you will get an estimate much faster.

I have actually tested this. It would take 45sec with just GPS, but under 7sec with WiFi.

Knowing Google's ethics (haha) they will definitely use this data also to advertise services to the people living there, as "now" they know exactly where you live and thus may push more relevant ads instead of a random store 500km away.

Your phone has a tiny antenna, unless you live out in the country you won’t have good sky view most of the time, and it takes time to get a fix. Most people open their phone and expect to know where they are within a few seconds.

For one, it can speed up finding your location if GPS is cold. Maps will start zeroing in by using wifi while GPS is heating up and then it gets the precise location from gps when it is available.

Googlers correct me on this, but from observation, that's how it seems to work.

(a) People walking around near your house with Android phones are constantly Wi-Fi scanning their environment, correlate Wi-Fi SSIDs and MAC addresses with GPS locations, and sending this info to Google

(b) When you or anyone else don't have a GPS signal because you're indoors, Google can run a Wi-Fi scan and geolocate you indoors from (a)

Also, s/Google/Apple/, s/Google/Mozilla/, they all do the same thing.

You can even run a Wi-Fi scan yourself with "sudo iwlist scanning", put the data in the appropriate format, and send it to Google's API [1] or Mozilla's API [2] for geolocation.

[1] https://developers.google.com/maps/documentation/geolocation...

[2] https://ichnaea.readthedocs.io/en/latest/api/geolocate.html#...

I don't know, but I imagine accelerometers work ok for cars on roads, but less so for meandering pedestrians in alleys and semi-enclosed shopping plazas.

I think those "downtown canyons" are likely to be the places where wifi information helps the most, so that would be my guess.

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