How Accurate Is Your Phone's Location History?

Outdoors, under open sky, a phone’s GPS position is usually within about 5 metres of where you are: the US government’s GPS.gov puts typical smartphone accuracy at a 4.9 m radius. Near tall buildings, under trees, and especially indoors, it gets worse, often by tens of metres, and when the phone falls back on Wi-Fi or cell towers, by a hundred metres or more. Each position comes with an estimate of its own error, and reading a location history well means taking that error into account.

Where the Position Comes From

A phone combines several ways of finding itself:

• Satellites (GPS and other systems). Accurate in the open. GPS.gov notes that accuracy worsens near buildings, bridges, and trees, and that signals blocked or reflected off walls (“multipath”) are a common cause of a wrong position. Indoors and underground, satellite signals may not reach the phone at all.
• Wi-Fi. The phone looks up nearby networks in a database of where they were seen. It works indoors, but less precisely.
• Cell towers. The coarsest, used when nothing better is available.

How much these differ was measured on the iPhone 3G by Zandbergen in 2009: a median error of about 8 m for assisted GPS, 74 m for Wi-Fi positioning, and 600 m for cell positioning. Phones have improved since, but the order hasn’t changed. A 2019 study of an iPhone 6 in an urban environment by Merry and Bettinger found an average horizontal error of 7 to 13 m, similar to recreation-grade GPS receivers where signals reflect off buildings.

What the Reported Accuracy Means

Each position a phone reports comes with an accuracy, a radius in metres around it. It isn’t a guarantee, but a confidence level, and not every platform uses the same one:

• Android reports the radius within which the true position lies with 68% confidence. So roughly one fix in three is farther off than its accuracy says.
• Browsers (the W3C Geolocation standard) report it at 95% confidence.

A position marked “±20 m” and one marked “±150 m” deserve very different trust. The second can’t tell your kitchen from your neighbour’s.

Why It Matters for What You Track

• Distance travelled. A phone lying still on a table still reports positions that wander within their error. Adding up every small jump between them turns a quiet day at home into kilometres of “movement”. Distance only means something once fixes that move less than their error are ignored.
• Stays. Indoor positions scatter, so a stay at one place shows as a cloud of fixes, not a point. Grouping fixes that stay within a radius of their centre for a while, the usual stay-point rule, is how a day’s places are found.
• Time at a place. A place drawn too tightly around your home misses the fixes that land across the street, and undercounts your time there. One drawn too wide catches the café next door.
• Gaps. A phone that is off, out of battery, or not allowed to track leaves a gap, and nothing in it says where you were.

Getting a Better History

• Keep location services on and allowed for the app that records it, so the history has fewer gaps.
• Expect indoor positions to be rough, and draw places generously: since Wi-Fi positions can be tens of metres off, a radius of about 100 m around a home or an office catches more of its fixes than one of 20 m.
• Judge a single surprising position by its accuracy before believing it.

Following It in Kaizora

Location History keeps each position with its accuracy, where its source gives one, from Kaizora’s own tracking (while the app is open, every 15 minutes or 50 metres, switched on per device), Google Maps Timeline, your photos, or positions you add. Distance Travelled counts a fix as movement only when it is farther from where you last were than the two positions’ accuracy explains, and adds nothing across gaps of more than a day. A stay is consecutive fixes within 200 metres of their centre for at least 15 minutes, and Time at Home and Time at Work add up the time between consecutive fixes inside your places of that kind, leaving out gaps of more than 16 hours. See Add Your Places and Track Your Location on This Device.

The Short Version

• Outdoors, a phone is typically within about 5 m; indoors and among tall buildings, tens of metres or more.
• Wi-Fi and cell positions are much rougher than GPS.
• The reported accuracy is a confidence radius: 68% on Android, 95% in browsers.
• Distance, stays, and time at places all need that error taken into account.

Sources

• GPS.gov, GPS Accuracy.
• Zandbergen PA, “Accuracy of iPhone locations: a comparison of assisted GPS, WiFi and cellular positioning,” Transactions in GIS 13, no. s1 (2009): 5–25. doi:10.1111/j.1467-9671.2009.01152.x
• Merry K, Bettinger P, “Smartphone GPS accuracy study in an urban environment,” PLOS ONE 14, no. 7 (2019): e0219890. doi:10.1371/journal.pone.0219890
• Android Developers, Location: getAccuracy().
• W3C, Geolocation.