Agent Skills: Core Location Reference

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)
    }
}

Part 11: Geocoding

CLGeocoder — Forward Geocoding (Address → Coordinate)

let geocoder = CLGeocoder()

func geocodeAddress(_ address: String) async throws -> CLLocation? {
    let placemarks = try await geocoder.geocodeAddressString(address)
    return placemarks.first?.location
}

// With locale for localized results
let placemarks = try await geocoder.geocodeAddressString(
    "1 Apple Park Way",
    in: nil,  // CLRegion hint (optional)
    preferredLocale: Locale(identifier: "en_US")
)

CLGeocoder — Reverse Geocoding (Coordinate → Address)

func reverseGeocode(_ location: CLLocation) async throws -> CLPlacemark? {
    let placemarks = try await geocoder.reverseGeocodeLocation(location)
    return placemarks.first
}

// Usage
if let placemark = try await reverseGeocode(location) {
    let street = placemark.thoroughfare          // "Apple Park Way"
    let city = placemark.locality                // "Cupertino"
    let state = placemark.administrativeArea     // "CA"
    let zip = placemark.postalCode               // "95014"
    let country = placemark.country              // "United States"
    let isoCountry = placemark.isoCountryCode    // "US"
}

CLPlacemark Key Properties

| Property | Example | Notes | |----------|---------|-------| | name | "Apple Park" | Location name | | thoroughfare | "Apple Park Way" | Street name | | subThoroughfare | "1" | Street number | | locality | "Cupertino" | City | | subLocality | "Silicon Valley" | Neighborhood | | administrativeArea | "CA" | State/province | | postalCode | "95014" | ZIP/postal code | | country | "United States" | Country name | | isoCountryCode | "US" | ISO country code | | timeZone | America/Los_Angeles | Time zone | | location | CLLocation | Coordinate |

Geocoding Rate Limits

• One request at a time — CLGeocoder throws if a request is in progress
• Apple rate-limits — Throttle to avoid kCLErrorGeocodeCanceled
• Cache results — Don't re-geocode the same address/coordinate
• Batch carefully — Add delays between sequential geocode requests

// Check if geocoder is busy
if geocoder.isGeocoding {
    geocoder.cancelGeocode()  // Cancel previous before starting new
}

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