Working with Location (expo-location)

1. Requesting Location Permissions

Permission	Description	Status	Usage
ACCESS_FINE_LOCATION	Allows access to precise location data	NEW	Required for high-accuracy geolocation
ACCESS_COARSE_LOCATION	Allows access to approximate location data	STABLE	Used for less precise location services

Example: Requesting Location Permissions

import * as Permissions from 'expo-permissions';
import * as Location from 'expo-location';

const requestLocationPermission = async () => {
  const { status } = await Permissions.askAsync(Permissions.LOCATION);
  if (status !== 'granted') {
    console.log('Permission to access location was denied');
    return false;
  }
  return true;
};

Note: On Android, you must also add the ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions to your app.json or app.config.js.

Warning: Users may deny location permissions, which can lead to incomplete or inaccurate geolocation data. Always handle permission denials gracefully.

2. Getting Current Position

Property	Description	Default	Notes
accuracy	Accuracy level of the location data	`10`	Higher values mean more accurate but slower results
distanceInterval	Minimum distance (in meters) to travel before updating location	`0`	Set to 0 for updates on every movement
heading	Include heading information in the result	`false`	Requires additional permissions on some platforms

Example: Requesting Current Position

import * as Location from 'expo-location';

const getCurrentLocation = async () => {
  try {
    const { coords } = await Location.getCurrentPositionAsync({
      accuracy: Location.Accuracy.High,
      distanceInterval: 10,
    });

    console.log("Latitude:", coords.latitude);
    console.log("Longitude:", coords.longitude);
  } catch (error) {
    console.error("Error getting location:", error);
  }
};

getCurrentLocation();

Note: The user must grant location permissions for this to work. On iOS, you need to add NSLocationWhenInUseUsageDescription or NSLocationAlwaysAndWhenInUseUsageDescription to your Info.plist.

Warning: On Android, you must request ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions at runtime.

3. Watching Position Changes

Property	Description	Values
watchPositionAsync	Starts watching for position changes	`Promise<Position>`
watchPositionAsync(options)	Options object to configure watching	`Object`

Example: Watching Position Changes

import * as Location from &#x27;expo-location&#x27;;

const watchPosition = async () => {
  const { coords } = await Location.watchPositionAsync(
    {
      accuracy: Location.Accuracy.High,
      distanceInterval: 10,
      timeInterval: 5000,
    },
    (location) => {
      console.log("New location:", location.coords);
    }
  );
};

watchPosition();

Note: The callback function will be called every time the location changes according to the specified interval.

Warning: Make sure to stop watching when no longer needed using Location.stopWatchingPositionAsync to prevent memory leaks.

Option	Description	Default Value	Notes
accuracy	Desired accuracy level	`Location.Accuracy.High`	Use `Location.Accuracy.Balanced` for lower power usage
distanceInterval	Minimum distance in meters to trigger a new position update	`10`	Set to 0 for updates on every change
timeInterval	Minimum time in milliseconds between updates	`5000`	Set to 0 for updates on every change

4. Reverse Geocoding

Reverse geocoding is the process of converting geographic coordinates (latitude and longitude) into human-readable addresses.

Property	Description	Example
location	Object containing latitude and longitude	`{ latitude: 40.7128, longitude: -74.0060 }`
locale	Locale to use for address formatting (optional)	`'en-US'`

Example: Reverse Geocoding

import * as Location from 'expo-location';

const address = await Location.reverseGeocodeAsync({
  latitude: 40.7128,
  longitude: -74.0060,
});

console.log(address[0].formattedAddress);
// Output: "123 Main St, New York, NY 10001, USA"

Note: The reverseGeocodeAsync function returns an array of address objects. The first object in the array is typically the most accurate match.

5. Forward Geocoding

Property	Description	Values
address	Address to geocode	`"1600 Amphitheatre Parkway, Mountain View, CA"`
latitude	Latitude of the location	`37.4223`
longitude	Longitude of the location	`-122.0843`

Example: Forward Geocoding an Address

import * as Location from 'expo-location';

const address = '1600 Amphitheatre Parkway, Mountain View, CA';
const geocoded = await Location.geocodeAsync(address);

console.log(geocoded[0]); // First geocoded result

Note: The geocodeAsync function returns an array of geocoded results. Each result includes latitude, longitude, and address components.

6. Setting Location Accuracy

Accuracy Level	Description	Use Case	Notes
HIGH_ACCURACY	Uses GPS and network-based location sources for the most precise location data.	Navigation, mapping, real-time tracking	May drain battery faster
MEDIUM_ACCURACY	Uses GPS and network-based location sources, but with reduced precision for better battery life.	General purpose apps, weather, local search	Recommended for most use cases
LOW_ACCURACY	Uses network-based location sources only (e.g., WiFi, cellular towers).	Basic location services, app launch tracking	Least battery drain, least accurate
PASSIVE	Uses location data from other apps running on the device.	Background tracking, analytics	No direct access to GPS; relies on other apps

Example: Setting Location Accuracy

import * as Location from 'expo-location';

await Location.requestPermissionsAsync();

const location = await Location.getCurrentPositionAsync({
  accuracy: Location.Accuracy.High,
});

console.log(location.coords.latitude, location.coords.longitude);

Note: The accuracy property is part of the LocationOptions object used in methods like getCurrentPositionAsync and watchPositionAsync.

7. Requesting Background Permissions

Permission	Description	Required in Manifest	Notes
ACCESS_FINE_LOCATION	Allows access to precise location data	Yes	Required for background location access
ACCESS_COARSE_LOCATION	Allows access to approximate location data	Yes	May be sufficient for some background use cases
ACCESS_BACKGROUND_LOCATION	Allows access to location in background	Yes	Must be declared in manifest for background use

Example: Requesting Background Location Permission

import * as Location from &#x27;expo-location&#x27;;

const requestBackgroundLocationPermission = async () => {
  const { status } = await Location.requestForegroundPermissionsAsync();
  if (status !== &#x27;granted&#x27;) {
    console.log(&#x27;Permission to access location was denied&#x27;);
    return;
  }

  // For background access, you may need to request separately
  const backgroundStatus = await Location.requestBackgroundPermissionsAsync();
  if (backgroundStatus.status !== &#x27;granted&#x27;) {
    console.log(&#x27;Permission to access location in background was denied&#x27;);
  }
};

Note: On Android, background location permissions require additional setup in AndroidManifest.xml and may need to be requested separately from foreground permissions.

Warning: Users must explicitly grant background location permission in system settings. The app cannot request it directly if the user has previously denied it.

8. Starting Location Updates

Method	Description	Notes
Location.watchPositionAsync()	Starts watching for location updates	Returns a subscription object to stop watching

Example: Starting Location Updates

import * as Location from 'expo-location';

const startLocationUpdates = async () => {
  const { granted } = await Location.requestForegroundPermissionsAsync();
  if (!granted) {
    console.log('Permission denied');
    return;
  }

  const subscription = await Location.watchPositionAsync(
    {
      accuracy: Location.Accuracy.High,
      distanceInterval: 10,
      timeInterval: 1000,
    },
    (location) => {
      console.log('New location:', location.coords);
    }
  );

  return subscription;
};

startLocationUpdates();

Note: Ensure you have the necessary permissions declared in your app's manifest and that the user has granted location access.

9. Getting Last Known Position

Property	Description	Example
getLastKnownPositionAsync	Retrieves the last known position of the device	`import * as Location from 'expo-location'; const lastPosition = await Location.getLastKnownPositionAsync(); console.log(lastPosition);`

Note: The last known position may be outdated or unavailable if the device has not moved recently.

10. Checking Location Services

Property	Description	Values
hasLocationPermission	Indicates if the app has location permission	`true` or `false`
hasBackgroundLocationPermission	Indicates if the app has background location permission	`true` or `false`
hasFineLocationPermission	Indicates if the app has fine location permission	`true` or `false`
hasCoarseLocationPermission	Indicates if the app has coarse location permission	`true` or `false`

Example: Check Location Permissions

import * as Location from 'expo-location';

const checkLocationPermissions = async () => {
  const { status } = await Location.requestForegroundPermissionsAsync();
  console.log("Location permission status:", status);
};

checkLocationPermissions();

Note: On Android, you must request ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions in your app's manifest.

Warning: On iOS, location permissions are requested at runtime. If the user denies permission, you must guide them to enable it in Settings.

11. Handling Location Errors

Error Type	Description	How to Handle
PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION	Permission denied for fine location access	Request permission again or guide user to enable in settings
PermissionsAndroid.PERMISSIONS.ACCESS_COARSE_LOCATION	Permission denied for coarse location access	Request permission again or guide user to enable in settings
ExpoLocation.PermissionDeniedError	User denied location permission	Inform user and provide steps to enable permissions
ExpoLocation.PositionUnavailableError	Location is unavailable (e.g., GPS is off)	Inform user to enable location services
ExpoLocation.TimeoutError	Location request timed out	Retry or inform user to try again later

Example: Handling Location Errors

import * as Location from 'expo-location';

try {
  const location = await Location.getCurrentPositionAsync({});
} catch (error) {
  if (error.code === 'PERMISSION_DENIED') {
    console.log("Location permission denied");
  } else if (error.code === 'POSITION_UNAVAILABLE') {
    console.log("Location is unavailable");
  } else if (error.code === 'TIMEOUT') {
    console.log("Location request timed out");
  } else {
    console.log("Unknown error: ", error.message);
  }
}

12. Using Heading Updates

Property	Description	Notes
heading	`number`	Current heading in degrees (0-360)
magneticHeading	`number`	Heading relative to magnetic north
trueHeading	`number`	Heading relative to true north
accuracy	`number`	Estimated accuracy of heading in degrees

import * as Location from 'expo-location';

const subscribeToHeading = async () => {
  const { granted } = await Location.requestForegroundPermissionsAsync();
  if (!granted) {
    console.log("Permission denied");
    return;
  }

  const subscription = await Location.watchHeadingAsync((heading) => {
    console.log("Heading:", heading);
  });

  // To stop watching:
  // subscription.remove();
};

subscribeToHeading();

Note: Heading updates are only available on devices with a compass sensor. On devices without a compass, the heading will be null.