GPS

rowan ~ Your iPhone 12 mini has built-in GPS, GLONASS, Galileo, QZSS, and BeiDou. Source:

iPhone 12 mini - Technical Specifications

...so you could look up the accuracy of those navigation systems. And if you're considering buying a new iPhone, only the iPhone 14 Pro models have "Precision dual-frequency GPS":

iPhone 14 Pro Models Feature Improved GPS Accuracy

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Improve GPS accuracy

GPS accuracy depends on the number of visible GPS satellites. Locating all visible satellites can take several minutes, with accuracy gradually increasing over time. To improve GPS accuracy:

• Make sure that you've set the date, time, and time zone correctly on the device in Settings > General > Date & Time. If possible, use Set Automatically.
• Keep a clear view in several directions. Walls, vehicle roofs, tall buildings, mountains, and other obstructions can block line of sight to GPS satellites. When this happens, your device uses Wi-Fi or cellular networks to determine your position until the GPS satellites are visible again.

rowan ~ what3words on the App Store shows "GPS Accuracy" when the compass is tapped:

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