Core Location Reference

Comprehensive API reference for modern Core Location (iOS 17+).

When to Use

• Need API signatures for CLLocationUpdate, CLMonitor, CLServiceSession
• Implementing geofencing or region monitoring
• Configuring background location updates
• Understanding authorization patterns
• Debugging location service issues

Related Skills

• axiom-core-location — Anti-patterns, decision trees, pressure scenarios
• axiom-core-location-diag — Symptom-based troubleshooting
• axiom-energy-ref — Location as battery subsystem (accuracy vs power)

---

Part 1: Modern API Overview (iOS 17+)

Four key classes replace legacy CLLocationManager patterns:

Class	Purpose	iOS
CLLocationUpdate	AsyncSequence for location updates	17+
CLMonitor	Condition-based geofencing/beacons	17+
CLServiceSession	Declarative authorization goals	18+
CLBackgroundActivitySession	Background location support	17+

Migration path: Legacy CLLocationManager still works, but new APIs provide:

• Swift concurrency (async/await)
• Automatic pause/resume
• Simplified authorization
• Better battery efficiency

---

Part 2: CLLocationUpdate API

Basic Usage

import CoreLocation

Task {
    do {
        for try await update in CLLocationUpdate.liveUpdates() {
            if let location = update.location {
                // Process location
            }
            if update.isStationary {
                break // Stop when user stops moving
            }
        }
    } catch {
        // Handle location errors
    }
}

LiveConfiguration Options

CLLocationUpdate.liveUpdates(.default)
CLLocationUpdate.liveUpdates(.automotiveNavigation)
CLLocationUpdate.liveUpdates(.otherNavigation)
CLLocationUpdate.liveUpdates(.fitness)
CLLocationUpdate.liveUpdates(.airborne)

Choose based on use case. If unsure, use .default or omit parameter.

Key Properties

Property	Type	Description
location	CLLocation?	Current location (nil if unavailable)
isStationary	Bool	True when device stopped moving
authorizationDenied	Bool	User denied location access
authorizationDeniedGlobally	Bool	Location services disabled system-wide
authorizationRequestInProgress	Bool	Awaiting user authorization decision
accuracyLimited	Bool	Reduced accuracy (updates every 15-20 min)
locationUnavailable	Bool	Cannot determine location
insufficientlyInUse	Bool	Can't request auth (not in foreground)

Automatic Pause/Resume

When device becomes stationary:

1. Final update delivered with isStationary = true and valid location
2. Updates pause (saves battery)
3. When device moves, updates resume with isStationary = false

No action required—happens automatically.

AsyncSequence Operations

// Get first location with speed > 10 m/s
let fastUpdate = try await CLLocationUpdate.liveUpdates()
    .first { $0.location?.speed ?? 0 > 10 }

// WARNING: Avoid filters that may never match (e.g., horizontalAccuracy < 1)

---

Part 3: CLMonitor API

Swift actor for monitoring geographic conditions and beacons.

Basic Geofencing

let monitor = await CLMonitor("MyMonitor")

// Add circular region
let condition = CLMonitor.CircularGeographicCondition(
    center: CLLocationCoordinate2D(latitude: 37.33, longitude: -122.01),
    radius: 100
)
await monitor.add(condition, identifier: "ApplePark")

// Await events
for try await event in monitor.events {
    switch event.state {
    case .satisfied:  // User entered region
        handleEntry(event.identifier)
    case .unsatisfied:  // User exited region
        handleExit(event.identifier)
    case .unknown:
        break
    @unknown default:
        break
    }
}

CircularGeographicCondition

CLMonitor.CircularGeographicCondition(
    center: CLLocationCoordinate2D,
    radius: CLLocationDistance  // meters, minimum ~100m effective
)

BeaconIdentityCondition

Three granularity levels:

// All beacons with UUID (any site)
CLMonitor.BeaconIdentityCondition(uuid: myUUID)

// Specific site (UUID + major)
CLMonitor.BeaconIdentityCondition(uuid: myUUID, major: 100)

// Specific beacon (UUID + major + minor)
CLMonitor.BeaconIdentityCondition(uuid: myUUID, major: 100, minor: 5)

Condition Limit

Maximum 20 conditions per app. Prioritize what to monitor. Swap regions dynamically based on user location if needed.

Adding with Assumed State

// If you know initial state
await monitor.add(condition, identifier: "Work", assuming: .unsatisfied)

Core Location will correct if assumption wrong.

Accessing Records

// Get single record
if let record = await monitor.record(for: "ApplePark") {
    let condition = record.condition
    let lastEvent = record.lastEvent
    let state = lastEvent.state
    let date = lastEvent.date
}

// Get all identifiers
let allIds = await monitor.identifiers

Event Properties

Property	Description
identifier	String identifier of condition
state	.satisfied, .unsatisfied, .unknown
date	When state changed
refinement	For wildcard beacons, actual UUID/major/minor detected
conditionLimitExceeded	Too many conditions (max 20)
conditionUnsupported	Condition type not available
accuracyLimited	Reduced accuracy prevents monitoring

Critical Requirements

1. One monitor per name — Only one instance with given name at a time
2. Always await events — Events only become lastEvent after handling
3. Reinitialize on launch — Recreate monitor in didFinishLaunchingWithOptions

---

Part 4: CLServiceSession API (iOS 18+)

Declarative authorization—tell Core Location what you need, not what to do.

Basic Usage

// Hold session for duration of feature
let session = CLServiceSession(authorization: .whenInUse)

for try await update in CLLocationUpdate.liveUpdates() {
    // Process updates
}

Authorization Requirements

CLServiceSession(authorization: .none)       // No auth request
CLServiceSession(authorization: .whenInUse)  // Request When In Use
CLServiceSession(authorization: .always)     // Request Always (must start in foreground)

Full Accuracy Request

// For features requiring precise location (e.g., navigation)
CLServiceSession(
    authorization: .whenInUse,
    fullAccuracyPurposeKey: "NavigationPurpose"  // Key in Info.plist
)

Requires NSLocationTemporaryUsageDescriptionDictionary in Info.plist.

Implicit Sessions

Iterating CLLocationUpdate.liveUpdates() or CLMonitor.events creates implicit session with .whenInUse goal.

To disable implicit sessions:

<!-- Info.plist -->
<key>NSLocationRequireExplicitServiceSession</key>
<true/>

Session Layering

Don't replace sessions—layer them:

// Base session for app
let baseSession = CLServiceSession(authorization: .whenInUse)

// Additional session when navigation feature active
let navSession = CLServiceSession(
    authorization: .whenInUse,
    fullAccuracyPurposeKey: "Nav"
)
// Both sessions active simultaneously

Diagnostic Properties

for try await diagnostic in session.diagnostics {
    if diagnostic.authorizationDenied {
        // User denied—offer alternative
    }
    if diagnostic.authorizationDeniedGlobally {
        // Location services off system-wide
    }
    if diagnostic.insufficientlyInUse {
        // Can't request auth (not foreground)
    }
    if diagnostic.alwaysAuthorizationDenied {
        // Always auth specifically denied
    }
    if !diagnostic.authorizationRequestInProgress {
        // Decision made (granted or denied)
        break
    }
}

Session Lifecycle

Sessions persist through:

• App backgrounding
• App suspension
• App termination (Core Location tracks)

On relaunch, recreate sessions immediately in didFinishLaunchingWithOptions.

---

Part 5: Authorization State Machine

Authorization Levels

Status	Description
.notDetermined	User hasn't decided
.restricted	Parental controls prevent access
.denied	User explicitly refused
.authorizedWhenInUse	Access while app active
.authorizedAlways	Background access

Accuracy Authorization

Value	Description
.fullAccuracy	Precise location
.reducedAccuracy	Approximate (~5km), updates every 15-20 min

Required Info.plist Keys

<!-- Required for When In Use -->
<key>NSLocationWhenInUseUsageDescription</key>
<string>We need your location to show nearby places</string>

<!-- Required for Always -->
<key>NSLocationAlwaysAndWhenInUseUsageDescription</key>
<string>We track your location to send arrival reminders</string>

<!-- Optional: default to reduced accuracy -->
<key>NSLocationDefaultAccuracyReduced</key>
<true/>

Legacy Authorization Pattern

@MainActor
class LocationManager: NSObject, CLLocationManagerDelegate {
    private let manager = CLLocationManager()

    func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
        switch manager.authorizationStatus {
        case .notDetermined:
            manager.requestWhenInUseAuthorization()
        case .authorizedWhenInUse, .authorizedAlways:
            enableLocationFeatures()
        case .denied, .restricted:
            disableLocationFeatures()
        @unknown default:
            break
        }
    }
}

---

Part 6: Background Location

Requirements

1. Background mode capability: Signing & Capabilities → Background Modes → Location updates
2. Info.plist: Adds UIBackgroundModes with location value
3. CLBackgroundActivitySession or LiveActivity

CLBackgroundActivitySession

// Create and HOLD reference (deallocation invalidates session)
var backgroundSession: CLBackgroundActivitySession?

func startBackgroundTracking() {
    // Must start from foreground
    backgroundSession = CLBackgroundActivitySession()

    Task {
        for try await update in CLLocationUpdate.liveUpdates() {
            processUpdate(update)
        }
    }
}

func stopBackgroundTracking() {
    backgroundSession?.invalidate()
    backgroundSession = nil
}

Background Indicator

Blue status bar/pill appears when:

• App authorized as "When In Use"
• App receiving location in background
• CLBackgroundActivitySession active

App Lifecycle

1. Foreground → Background: Session continues
2. Background → Suspended: Session preserved, updates pause
3. Suspended → Terminated: Core Location tracks session
4. Terminated → Background launch: Recreate session immediately

func application(_ application: UIApplication,
                 didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Recreate background session if was tracking
    if wasTrackingLocation {
        backgroundSession = CLBackgroundActivitySession()
        startLocationUpdates()
    }
    return true
}

---

Part 7: Legacy APIs (iOS 12-16)

CLLocationManager Delegate Pattern

class LocationManager: NSObject, CLLocationManagerDelegate {
    private let manager = CLLocationManager()

    override init() {
        super.init()
        manager.delegate = self
        manager.desiredAccuracy = kCLLocationAccuracyBest
        manager.distanceFilter = 10 // meters
    }

    func startUpdates() {
        manager.startUpdatingLocation()
    }

    func stopUpdates() {
        manager.stopUpdatingLocation()
    }

    func locationManager(_ manager: CLLocationManager,
                        didUpdateLocations locations: [CLLocation]) {
        guard let location = locations.last else { return }
        // Process location
    }
}

Accuracy Constants

Constant	Accuracy	Battery Impact
kCLLocationAccuracyBestForNavigation	~5m	Highest
kCLLocationAccuracyBest	~10m	Very High
kCLLocationAccuracyNearestTenMeters	~10m	High
kCLLocationAccuracyHundredMeters	~100m	Medium
kCLLocationAccuracyKilometer	~1km	Low
kCLLocationAccuracyThreeKilometers	~3km	Very Low
kCLLocationAccuracyReduced	~5km	Lowest

Legacy Region Monitoring

// Deprecated in iOS 17, use CLMonitor instead
let region = CLCircularRegion(
    center: coordinate,
    radius: 100,
    identifier: "MyRegion"
)
region.notifyOnEntry = true
region.notifyOnExit = true
manager.startMonitoring(for: region)

Significant Location Changes

Low-power alternative for coarse tracking:

manager.startMonitoringSignificantLocationChanges()
// Updates ~500m movements, works in background

Visit Monitoring

Detect arrivals/departures:

manager.startMonitoringVisits()

func locationManager(_ manager: CLLocationManager, didVisit visit: CLVisit) {
    let arrival = visit.arrivalDate
    let departure = visit.departureDate
    let coordinate = visit.coordinate
}

---

Part 8: Geofencing Best Practices

Region Size

• Minimum effective radius: ~100 meters
• Smaller regions: May not trigger reliably
• Larger regions: More reliable but less precise

20-Region Limit Strategy

// Dynamic region management
func updateMonitoredRegions(userLocation: CLLocation) async {
    let nearbyPOIs = fetchNearbyPOIs(around: userLocation, limit: 20)

    // Remove old regions
    for id in await monitor.identifiers {
        if !nearbyPOIs.contains(where: { $0.id == id }) {
            await monitor.remove(id)
        }
    }

    // Add new regions
    for poi in nearbyPOIs {
        let condition = CLMonitor.CircularGeographicCondition(
            center: poi.coordinate,
            radius: 100
        )
        await monitor.add(condition, identifier: poi.id)
    }
}

Entry/Exit Timing

• Entry: Usually within seconds to minutes
• Exit: May take 3-5 minutes after leaving
• Accuracy depends on: Cell towers, WiFi, GPS availability

Persistence

• Conditions persist across app launches
• Must reinitialize monitor with same name on launch
• Core Location wakes app for events

---

Part 9: Testing and Simulation

Xcode Location Simulation

1. Run on simulator
2. Debug → Simulate Location → Choose location
3. Or use custom GPX file

Custom GPX Route

<?xml version="1.0"?>
<gpx version="1.1">
    <wpt lat="37.331686" lon="-122.030656">
        <time>2024-01-01T00:00:00Z</time>
    </wpt>
    <wpt lat="37.332686" lon="-122.031656">
        <time>2024-01-01T00:00:10Z</time>
    </wpt>
</gpx>

Testing Authorization States

Settings → Privacy & Security → Location Services:

• Toggle app authorization
• Toggle system-wide location services
• Test reduced accuracy

Console Filtering

# Filter location logs
log stream --predicate 'subsystem == "com.apple.locationd"'

---

Part 10: Swift Concurrency Integration

Task Cancellation

let locationTask = Task {
    for try await update in CLLocationUpdate.liveUpdates() {
        if Task.isCancelled { break }
        processUpdate(update)
    }
}

// Later
locationTask.cancel()

MainActor Considerations

@MainActor
class LocationViewModel: ObservableObject {
    @Published var currentLocation: CLLocation?

    func startTracking() {
        Task {
            for try await update in CLLocationUpdate.liveUpdates() {
                // Already on MainActor, safe to update @Published
                self.currentLocation = update.location
            }
        }
    }
}

Error Handling

Task {
    do {
        for try await update in CLLocationUpdate.liveUpdates() {
            if update.authorizationDenied {
                throw LocationError.authorizationDenied
            }
            processUpdate(update)
        }
    } catch {
        handleError(error)
    }
}

---

Troubleshooting Quick Reference

Symptom	Check
No location updates	Authorization status, Info.plist keys
Background not working	Background mode capability, CLBackgroundActivitySession
Always auth not effective	CLServiceSession with .always, started in foreground
Geofence not triggering	Region count (max 20), radius (min ~100m)
Reduced accuracy only	Check accuracyAuthorization, request temporary full accuracy
Location icon stays on	Ensure stopUpdatingLocation() or break from async loop

---

Resources

WWDC: 2023-10180, 2023-10147, 2024-10212

Docs: /corelocation, /corelocation/clmonitor, /corelocation/cllocationupdate, /corelocation/clservicesession

Skills: axiom-core-location, axiom-core-location-diag, axiom-energy-ref