Core Location Patterns

Discipline skill for Core Location implementation decisions. Prevents common authorization mistakes, battery drain, and background location failures.

When to Use

• Choosing authorization strategy (When In Use vs Always)
• Deciding monitoring approach (continuous vs significant-change vs CLMonitor)
• Implementing geofencing or background location
• Debugging "location not working" issues
• Reviewing location code for anti-patterns

Related Skills

• axiom-core-location-ref — API reference, code examples
• axiom-core-location-diag — Symptom-based troubleshooting
• axiom-energy — Location as battery subsystem

---

Part 1: Anti-Patterns (with Time Costs)

Anti-Pattern 1: Premature Always Authorization

Wrong (30-60% denial rate):

// First launch: "Can we have Always access?"
manager.requestAlwaysAuthorization()

Right (5-10% denial rate):

// Start with When In Use
CLServiceSession(authorization: .whenInUse)

// Later, when user triggers background feature:
CLServiceSession(authorization: .always)

Time cost: 15 min to fix code, but 30-60% of users permanently denied = feature adoption destroyed.

Why: Users deny aggressive requests. Start minimal, upgrade when user understands value.

---

Anti-Pattern 2: Continuous Updates for Geofencing

Wrong (10x battery drain):

for try await update in CLLocationUpdate.liveUpdates() {
    if isNearTarget(update.location) {
        triggerGeofence()
    }
}

Right (system-managed, low power):

let monitor = await CLMonitor("Geofences")
let condition = CLMonitor.CircularGeographicCondition(
    center: target, radius: 100
)
await monitor.add(condition, identifier: "Target")

for try await event in monitor.events {
    if event.state == .satisfied { triggerGeofence() }
}

Time cost: 5 min to refactor, saves 10x battery.

---

Anti-Pattern 3: Ignoring Stationary Detection

Wrong (wasted battery):

for try await update in CLLocationUpdate.liveUpdates() {
    processLocation(update.location)
    // Never stops, even when device stationary
}

Right (automatic pause/resume):

for try await update in CLLocationUpdate.liveUpdates() {
    if let location = update.location {
        processLocation(location)
    }
    if update.isStationary, let location = update.location {
        // Device stopped moving - updates pause automatically
        // Will resume when device moves again
        saveLastKnownLocation(location)
    }
}

Time cost: 2 min to add check, saves significant battery.

---

Anti-Pattern 4: No Graceful Denial Handling

Wrong (broken UX):

for try await update in CLLocationUpdate.liveUpdates() {
    guard let location = update.location else { continue }
    // User denied - silent failure, no feedback
}

Right (graceful degradation):

for try await update in CLLocationUpdate.liveUpdates() {
    if update.authorizationDenied {
        showManualLocationPicker()
        break
    }
    if update.authorizationDeniedGlobally {
        showSystemLocationDisabledMessage()
        break
    }
    if let location = update.location {
        processLocation(location)
    }
}

Time cost: 10 min to add handling, prevents confused users.

---

Anti-Pattern 5: Wrong Accuracy for Use Case

Wrong (battery drain for weather app):

// Weather app using navigation accuracy
CLLocationUpdate.liveUpdates(.automotiveNavigation)

Right (match accuracy to need):

// Weather: city-level is fine
CLLocationUpdate.liveUpdates(.default)  // or .fitness for runners

// Navigation: needs high accuracy
CLLocationUpdate.liveUpdates(.automotiveNavigation)

Use Case	Configuration	Accuracy	Battery
Navigation	.automotiveNavigation	~5m	Highest
Fitness tracking	.fitness	~10m	High
Store finder	.default	~10-100m	Medium
Weather	.default	~100m+	Low

Time cost: 1 min to change, significant battery savings.

---

Anti-Pattern 6: Not Stopping Updates

Wrong (battery drain, location icon persists):

func viewDidLoad() {
    Task {
        for try await update in CLLocationUpdate.liveUpdates() {
            updateMap(update.location)
        }
    }
}
// User navigates away, updates continue forever

Right (cancel when done):

private var locationTask: Task<Void, Error>?

func startTracking() {
    locationTask = Task {
        for try await update in CLLocationUpdate.liveUpdates() {
            if Task.isCancelled { break }
            updateMap(update.location)
        }
    }
}

func stopTracking() {
    locationTask?.cancel()
    locationTask = nil
}

Time cost: 5 min to add cancellation, stops battery drain.

---

Anti-Pattern 7: Ignoring CLServiceSession (iOS 18+)

Wrong (procedural authorization juggling):

func requestAuth() {
    switch manager.authorizationStatus {
    case .notDetermined:
        manager.requestWhenInUseAuthorization()
    case .authorizedWhenInUse:
        if needsFullAccuracy {
            manager.requestTemporaryFullAccuracyAuthorization(...)
        }
    // Complex state machine...
    }
}

Right (declarative goals):

// Just declare what you need - Core Location handles the rest
let session = CLServiceSession(authorization: .whenInUse)

// For feature needing full accuracy
let navSession = CLServiceSession(
    authorization: .whenInUse,
    fullAccuracyPurposeKey: "Navigation"
)

// Monitor diagnostics if needed
for try await diag in session.diagnostics {
    if diag.authorizationDenied { handleDenial() }
}

Time cost: 30 min to migrate, simpler code, fewer bugs.

---

Part 2: Decision Trees

Authorization Strategy

Q1: Does your feature REQUIRE background location?
├─ NO → Use .whenInUse
│   └─ Q2: Does any feature need precise location?
│       ├─ ALWAYS → Add fullAccuracyPurposeKey to session
│       └─ SOMETIMES → Layer full-accuracy session when feature active
│
└─ YES → Start with .whenInUse, upgrade to .always when user triggers feature
    └─ Q3: When does user first need background location?
        ├─ IMMEDIATELY (e.g., fitness tracker) → Request .always on first relevant action
        └─ LATER (e.g., geofence reminders) → Add .always session when user creates first geofence

Monitoring Strategy

Q1: What are you monitoring for?
├─ USER POSITION (continuous tracking)
│   └─ Use CLLocationUpdate.liveUpdates()
│       └─ Q2: What activity?
│           ├─ Driving navigation → .automotiveNavigation
│           ├─ Walking/cycling nav → .otherNavigation
│           ├─ Fitness tracking → .fitness
│           ├─ Airplane apps → .airborne
│           └─ General → .default or omit
│
├─ ENTRY/EXIT REGIONS (geofencing)
│   └─ Use CLMonitor with CircularGeographicCondition
│       └─ Note: Maximum 20 conditions per app
│
├─ BEACON PROXIMITY
│   └─ Use CLMonitor with BeaconIdentityCondition
│       └─ Choose granularity: UUID only, UUID+major, UUID+major+minor
│
└─ SIGNIFICANT CHANGES ONLY (lowest power)
    └─ Use startMonitoringSignificantLocationChanges() (legacy)
        └─ Updates ~500m movements, works in background

Accuracy Selection

Q1: What's the minimum accuracy that makes your feature work?
├─ TURN-BY-TURN NAV needs 5-10m → .automotiveNavigation / .otherNavigation
├─ FITNESS TRACKING needs 10-20m → .fitness
├─ STORE FINDER needs 100m → .default
├─ WEATHER/CITY needs 1km+ → .default (reduced accuracy acceptable)
└─ GEOFENCING uses system determination → CLMonitor handles it

Q2: Will user be moving fast?
├─ DRIVING (high speed) → .automotiveNavigation (extra processing for speed)
├─ CYCLING/WALKING → .otherNavigation
└─ STATIONARY/SLOW → .default

Always start with lowest acceptable accuracy. Higher accuracy = higher battery drain.

---

Part 3: Pressure Scenarios

Scenario 1: "Just Use Always Authorization"

Context: PM says "Users want location reminders. Just request Always access on first launch so it works."

Pressure: Ship fast, seems simpler.

Reality:

• 30-60% of users will deny Always authorization when asked upfront
• Users who deny can only re-enable in Settings (most won't)
• Feature adoption destroyed before users understand value

Response:

"Always authorization has 30-60% denial rates when requested upfront. We should start with When In Use, then request Always upgrade when the user creates their first location reminder. This gives us a 5-10% denial rate because users understand why they need it."

Evidence: Apple's own guidance in WWDC 2024-10212: "CLServiceSessions should be taken proactively... hold one requiring full-accuracy when people engage a feature that would warrant a special ask for it."

---

Scenario 2: "Location Isn't Working in Background"

Context: QA reports "App stops getting location when backgrounded."

Pressure: Quick fix before release.

Wrong fixes:

• Add all background modes
• Use allowsBackgroundLocationUpdates = true without understanding
• Request Always authorization

Right diagnosis:

1. Check background mode capability exists
2. Check CLBackgroundActivitySession is held (not deallocated)
3. Check session started from foreground
4. Check authorization level (.whenInUse works with CLBackgroundActivitySession)

Response:

"Background location requires specific setup. Let me check: (1) Background mode capability, (2) CLBackgroundActivitySession held during tracking, (3) session started from foreground. Missing any of these causes silent failure."

Checklist:

// 1. Signing & Capabilities → Background Modes → Location updates
// 2. Hold session reference (property, not local variable)
var backgroundSession: CLBackgroundActivitySession?

func startBackgroundTracking() {
    // 3. Must start from foreground
    backgroundSession = CLBackgroundActivitySession()
    startLocationUpdates()
}

---

Scenario 3: "Geofence Events Aren't Firing"

Context: Geofences work in testing but not in production for some users.

Pressure: "It works on my device" dismissal.

Common causes:

1. Too many conditions: Maximum 20 per app
2. Radius too small: Minimum ~100m for reliable triggering
3. Overlapping regions: Can cause confusion
4. Not awaiting events: Events only become lastEvent after handled
5. Not reinitializing on launch: Monitor must be recreated

Response:

"Geofencing has several system constraints. Check: (1) Are we within the 20-condition limit? (2) Are all radii at least 100m? (3) Is the app reinitializing CLMonitor on launch? (4) Is the app always awaiting on monitor.events?"

Diagnostic code:

// Check condition count
let count = await monitor.identifiers.count
if count >= 20 {
    print("At 20-condition limit!")
}

// Check all conditions
for id in await monitor.identifiers {
    if let record = await monitor.record(for: id) {
        let condition = record.condition
        if let geo = condition as? CLMonitor.CircularGeographicCondition {
            if geo.radius < 100 {
                print("Radius too small: \(id)")
            }
        }
    }
}

---

Part 4: Checklists

Pre-Release Location Checklist

Info.plist:

• NSLocationWhenInUseUsageDescription with clear explanation
• NSLocationAlwaysAndWhenInUseUsageDescription if using Always (clear why background needed)
• NSLocationDefaultAccuracyReduced if reduced accuracy acceptable
• NSLocationTemporaryUsageDescriptionDictionary if requesting temporary full accuracy
• UIBackgroundModes includes location if background tracking

Authorization:

• Start with minimal authorization (.whenInUse)
• Upgrade to .always only when user triggers background feature
• Handle authorization denial gracefully (offer alternatives)
• Handle global location services disabled
• Test with reduced accuracy authorization

Updates:

• Using appropriate LiveConfiguration for use case
• Handling isStationary for pause/resume
• Cancelling location tasks when feature inactive
• Not using continuous updates for geofencing

Testing:

• Tested authorization denial flow
• Tested reduced accuracy mode
• Tested background-to-foreground transitions
• Tested app termination and relaunch recovery

Background Location Checklist

Setup:

• Background mode capability added (Location updates)
• CLBackgroundActivitySession created and HELD (not local variable)
• Session started from foreground
• Updates restarted on background launch in didFinishLaunchingWithOptions

Authorization:

• Using .whenInUse with CLBackgroundActivitySession, OR
• Using .always (but only if needed beyond background indicator)

Lifecycle:

• Persisting "was tracking" state for relaunch recovery
• Recreating CLBackgroundActivitySession on background launch
• Restarting CLLocationUpdate iteration on launch
• CLMonitor reinitialized with same name on launch

Testing:

• Blue background location indicator appears when backgrounded
• Updates continue when app backgrounded
• Updates resume after app suspended and resumed
• Updates resume after app terminated and relaunched

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Part 5: iOS Version Considerations

Feature	iOS Version	Notes
CLLocationUpdate	iOS 17+	AsyncSequence API
CLMonitor	iOS 17+	Replaces CLCircularRegion
CLBackgroundActivitySession	iOS 17+	Background with blue indicator
CLServiceSession	iOS 18+	Declarative authorization
Implicit service sessions	iOS 18+	From iterating liveUpdates
CLLocationManager	iOS 2+	Legacy but still works

For iOS 14-16 support: Use CLLocationManager delegate pattern (see core-location-ref Part 7).

For iOS 17+: Prefer CLLocationUpdate and CLMonitor.

For iOS 18+: Add CLServiceSession for declarative authorization.

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Resources

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

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

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