How do I know which is the default measure system (imperial or metric) on iOS?

Question

How do I know which is the default measure system (imperial or metric) on iOS ?

How do I get this preference from the device settings, so I know what to display in m

Answer 1

As others mentioned before, the UK uses a mix of metric and imperial units.

I would recommend using the new MeassurementFormatter introduced in iOS 10 which handles most of these discrepancies:

import Foundation

let locale = Locale(identifier: "EN_UK")
locale.usesMetricSystem // true!
var formatter = MeasurementFormatter()
formatter.locale = locale
formatter.string(from: Measurement(value: 1000, unit: UnitLength.meters)) // 0.621 mi

To render a distance as a string in local, natural unit, use:

let distanceInMeters: CLLocationDistance = 1000
let formatter = MeasurementFormatter()
formatter.string(from: Measurement(value: distanceInMeters, unit: UnitLength.meters)) // 0.621 mi

Official documentation: https://developer.apple.com/documentation/foundation/measurementformatter