Use Maps Offline

With preloaded offline maps you can access whole countries or even continents completely offline without using any internet connection or consuming OTA bandwith.

Offline maps (also known as persistent maps) offer the same features as the map data that is available online: You can search for places, calculate routes, start guidance (only available for the Navigate Edition), and - of course - you can interact with the map in the same way as with online map data.

Two engines support offline map data:

• Use the OfflineSearchEngine as equivalent to the online operable SearchEngine to search for places.
• Use the OfflineRoutingEngine as equivalent to the online operable RoutingEngine to calculate routes.

Note that the above engines need to be executed on already downloaded or cached map data to make use of offline features. Other engines will not return results when they are executed offline - even if offline data is available.

In addition, the Navigator and the VisualNavigator work fully with offline map data to support offline turn-by-turn guidance. Worth to mention: The Navigator works headless (without a MapView), but it also requires map data to deliver events.

Once a Region has been downloaded with the MapDownloader - or when an area has been cached by panning the map - the MapView is fully operable for this area without an internet connection.

Below we describe how to get offline map data integrated into your application with the MapDownloader.

Why use offline maps? There can be situations when an internet connection may lag, drop - or is completely off for a longer time. Especially, while on-the-go, a stable connection may not always be available. A mobile device may also be offline due to the user's decision to save bandwidth. This means: There can be multiple reasons to use offline maps - and last but not least, offline maps will speed up the user's experience with unbeatable response times. However, in most situations - when limited bandwidth and data consumption is not an issue - accessing online map data offers more accurate and up-to-date map data. Also, some features may not be available on offline maps, for example, search results may contain not all data that is available online.

You have two ways to access map data offline:

• Local Cache: By default, all map data is cached onto the device while using the map. This storage is persisted between sessions, but the storage size is limited and old cache data may be replaced with newer map data. Note: You can change the default cache path and the size with the SDKOptions you can pass into the SDKNativeEngine when you initialize the HERE SDK programmatically. Cached map data is stored in the map cache storage.

• Offline Maps: With offline maps you can download entire regions or even continents to preload their map data for offline use - including places, routing and other data. A dedicated MapDownloader enables you to get and to maintain this data. Offline maps data is persisted between sessions and the data will not be deleted unless the user decides so. Offline maps are stored in the persistent map storage.

Good to know:

When interacting with a map view, the HERE SDK will automatically make use of online data, the local map cache and the persistent map storage to provide the best possible user experience.
<!-- If a device is online, offline maps data will not be used while interacting with a map view and instead the local map cache storage will be used. If no cached data is available, new data will be downloaded into the cache. When the cache is full, a least recently used (LRU)) strategy is applied.

If a device is offline:

1. While interacting with a map view, the HERE SDK will first check if map data can be shown from the map cache storage.
2. If no cached data is available for the current target, the HERE SDK will look for offline maps data in the persistent map storage.
3. If no regions for offline usage have been downloaded, the map will be shown with less details or even no details. -->

Overview

Downloading and using offline maps can be achieved in two simple steps.

1) Download a list of Region objects. Optionally, this list can be localized with local region names. Once you have this list, you can pick the RegionId you want to download and pass it as download request to the MapDownloader.

2) Use the MapDownloader to download a single Region or a list of regions. You can also download several regions in parallel. Show the download progress to the user by setting a DownloadRegionsStatusListener.

Once the download has completed, the map is ready to be used. If a device is offline, it will automatically show the downloaded region when the camera's target is pointed to that region.

Since map data for regions, countries or whole continents can contain several hundreds of megabytes, a download may take a while - depending on factors such as available bandwidth. A download may also fail, when a connection gets timed out and cannot recover. For best user experience, it is recommended to allow the user to cancel ongoing operations and to watch the progress until a map download succeeds.

Create a MapDownloader Instance

You can create the MapDownloader once per SDKNativeEngine:

SDKNativeEngine? sdkNativeEngine = SDKNativeEngine.sharedInstance;
if (sdkNativeEngine == null) {
  throw ("SDKNativeEngine not initialized.");
}

_mapDownloader = MapDownloader.fromSdkEngine(sdkNativeEngine);

Usually, the SDKNativeEngine is automatically initialized when you start the app to show a MapView. Therefore, you can access it's instance at runtime and obtain the MapDownloader from it.

By default, the downloaded map data will be stored to a default location:

// Note that the default storage path can be adapted when creating a new SDKNativeEngine.
String storagePath = sdkNativeEngine.options.cachePath;
_showDialog("This example allows to download the region Switzerland.", "Storage path: $storagePath");

As stated in the comment, you can change that storage location, if you wish so - but then you need to create a new SDKNativeEngine instance as shown in the Key Concepts section and set the new cache path together with your credentials as part of the SDKOptions. Note that the storage path is unique for your credentials key.

Download a List of Regions

Each downloadable Region is identified by a unique RegionId. In order to know, which regions are available and which RegionID belongs to which Region, you need to download a list of all available offline maps. This contains regions from the entire world.

The code below downloads the list of downloadable regions and stores the available Region elements in a list for later use:

// Download a list of Region items that will tell us what map regions are available for later download.
_mapDownloader.getDownloadableRegionsWithLanguageCode(LanguageCode.deDe,
    (MapLoaderError? mapLoaderError, List<Region>? list) {
  if (mapLoaderError != null) {
    _showDialog("Error", "Downloadable regions error: $mapLoaderError");
    return;
  }

  // If error is null, it is guaranteed that the list will not be null.
  _downloadableRegions = list!;

  for (Region region in _downloadableRegions) {
    print("RegionsCallback: " + region.name);
    List<Region>? childRegions = region.childRegions;
    if (childRegions == null) {
      continue;
    }

    // Note that this code ignores to list the children of the children (and so on).
    for (Region childRegion in childRegions) {
      var sizeOnDiskInMB = childRegion.sizeOnDiskInBytes / (1024 * 1024);
      String logMessage = "Child region: " +
          childRegion.name +
          ", ID: " +
          childRegion.regionId.id.toString() +
          ", Size: " +
          sizeOnDiskInMB.toString() +
          " MB";
      print("RegionsCallback: " + logMessage);
    }
  }

  var listLenght = _downloadableRegions.length;
  _showDialog("Contintents found: $listLenght", "Each continent contains various countries. See log for details.");
});

Each region can contain child regions. For example, Europe contains Germany, France and Switzerland - and many more child regions. The sizeOnDiskInBytes parameter tells you how much space the downloaded map will occupy on the device's file system when it's uncompressed after download has completed. It makes sense to show this to the user before starting the download - as the available space on a device may be limited.

Download a Region

Once you know the RegionId, you can use it to start downloading the map data. Each Region instance contains a localized name and other data, such as the size of the downloaded map. When the map data is downloaded, all data is compressed and will be unpacked automatically onto the device's disk once the download is complete.

Below we search the downloaded list of regions to find the Region element for Switzerland. Note that we have requested the region list to be localized in German in the step above:

// Finds a region in the downloaded region list.
// Note that we ignore children of children (and so on): For example, a country may contain downloadable sub regions.
// For this example, we just download the country including possible sub regions.
Region? _findRegion(String localizedRegionName) {
  Region? downloadableRegion;
  for (Region region in _downloadableRegions) {
    if (region.name == localizedRegionName) {
      downloadableRegion = region;
      break;
    }

    List<Region>? childRegions = region.childRegions;
    if (childRegions == null) {
      continue;
    }

    for (Region childRegion in childRegions) {
      if (childRegion.name == localizedRegionName) {
        downloadableRegion = childRegion;
        break;
      }
    }
  }

  return downloadableRegion;
}

Once we know the Region, we can use it's RegionId to start the download. We pass the unique ID into a list, so we can download multiple regions with the same request. Here, we download only one region:

// Find region for Switzerland using the German name as identifier.
// Note that we requested the list of regions in German above.
String swizNameInGerman = "Schweiz";
Region? region = _findRegion(swizNameInGerman);

if (region == null) {
  _showDialog("Error", "Error: The Swiz region was not found. Click 'Get Regions' first.");
  return;
}

// For this example we download only one country.
List<RegionId> regionIDs = [region.regionId];

MapDownloaderTask mapDownloaderTask = _mapDownloader.downloadRegions(
    regionIDs,
    DownloadRegionsStatusListener((MapLoaderError? mapLoaderError, List<RegionId>? list) {
      // Handle events from onDownloadRegionsComplete().
      if (mapLoaderError != null) {
        _showDialog("Error", "Download regions completion error: $mapLoaderError");
        return;
      }

      // If error is null, it is guaranteed that the list will not be null.
      // For this example we downloaded only one hardcoded region.
      String message = "Download Regions Status: Completed 100% for Switzerland! ID: " + list!.first.id.toString();
      print(message);
    }, (RegionId regionId, int percentage) {
      // Handle events from onProgress().
      String message =
          "Download of Switzerland. ID: " + regionId.id.toString() + ". Progress: " + percentage.toString() + "%.";
      print(message);
    }, (MapLoaderError? mapLoaderError) {
      // Handle events from onPause().
      if (mapLoaderError == null) {
        _showDialog("Info", "The download was paused by the user calling mapDownloaderTask.pause().");
      } else {
        _showDialog("Error",
            "Download regions onPause error. The task tried to often to retry the download: $mapLoaderError");
      }
    }, () {
      // Hnadle events from onResume().
      _showDialog("Info", "A previously paused download has been resumed.");
    }));

_mapDownloaderTasks.add(mapDownloaderTask);

The DownloadRegionsStatusListener provides four events. The second one tells us the progress while the download is ongoing, while the first one notifies once the download has completed. Note that the download can also complete with a MapLoaderError, so it's worth to check if something went wrong.

The pause event notfies when a download was paused by the user or the task itself. Internally, the HERE SDK will retry to download a region when it was interrupted, ie. due to a bad network connection. If this happens too often, the MapLoaderError for lambda_onPause() is populated and the download pauses. A paused MapDownloaderTask can only be resumed by the user, which will be also indicated by the related event. Especially for larger regions it may be convenient to pause a download until the connection gets better, for example. When resumed, the download will continue at the progress where it stopped and no already downloaded map data will be lost. Note that calling downloadRegions() for a paused region will have the same effect as calling resume() on the original task and the progress will continue where it left off.

After kicking off the download, we get an immediate return value to be able to cancel the ongoing asynchronous download operation. Above, we store the MapDownloaderTask into a list, as a user might trigger the above code multiple times.

To cancel all ongoing downloads, you can use the following code snippet:

for (MapDownloaderTask mapDownloaderTask in _mapDownloaderTasks) {
  mapDownloaderTask.cancel();
}
int taskLength = _mapDownloaderTasks.length;
_showDialog("Note", "Cancelled $taskLength download tasks in list.");
_mapDownloaderTasks.clear();

Note that a MapDownloaderTask that was cancelled cannot be resumed again, but you can start a fresh download request again.

A usage example is available on GitHub as part of the offline_maps_app example app.

Update Map Data and Map Version

With the MapUpdater class you can check if newer map versions are available and - if available - update the already installed regions. Each HERE SDK version comes hardcoded with a specific map version. This defines the map data in the cache and the downloaded regions (if any).

Note that certain HERE SDK features may require a specific map version - as indicated in the related API Reference documentation or in this guide.

When an app update is installed that integrates a new HERE SDK version, it will most likely also feature a new map version. However, the map data will not be automatically updated, unless the MapUpdater is used to perform this task. Of course, map updates can also be installed for older HERE SDK versions.

• Check the currently used map version by calling mapUpdater.getCurrentMapVersion().
• Check if an update is available by calling mapUpdater.checkMapUpdate().

By calling mapUpdater.performMapUpdate() you can download and install the latest map data. An example for this is shown in the offline_maps_app example app on GitHub.

If no offline maps have been installed, calling mapUpdater.performMapUpdate() will only clear the cache and the cache will be subsequently filled with new data for the latest available map version.

The cache will always use the same map version as offline maps. If offline maps are updated, the cache will be also updated. The cache version will never be older than the offline maps version.

Note that it is not possible to enforce a map update by uninstalling all downloaded regions via deleteRegions() and then downloading the desired regions again. In that case, the same map version would be downloaded. However, if performMapUpdate() is executed beforehand then a map update may be indicated and can be installed.

Repair Broken Maps

It is not recommended to keep downloading or updating map data while an app is running in background. However, it may happen that an app gets closed before a map update operation can be completed - for example, due to a crash. So, in worst case an intermediate state may occur on the disk of the device.

The HERE SDK provides a convenient way to check for such issues with the getInitialPersistentMapStatus() method. It also allows to repair a broken map - if possible.

_checkInstallationStatus() {
  // Note that this value will not change during the lifetime of an app.
  PersistentMapStatus persistentMapStatus = _mapDownloader.getInitialPersistentMapStatus();
  if (persistentMapStatus != PersistentMapStatus.ok) {
    // Something went wrong after the app was closed the last time. It seems the offline map data is
    // corrupted. This can eventually happen, when an ongoing map download was interrupted due to a crash.
    print("PersistentMapStatus: The persistent map data seems to be corrupted. Trying to repair.");

    // Let's try to repair.
    _mapDownloader.repairPersistentMap((PersistentMapRepairError? persistentMapRepairError) {
      if (persistentMapRepairError == null) {
        print("RepairPersistentMap: Repair operation completed successfully!");
        return;
      }

      print("RepairPersistentMap: Repair operation failed: " + persistentMapRepairError.toString());
    });
  }
}

Either way, it is recommended to inform the user that there might be an issue with the downloaded map data. In worst case, the map data needs to be removed and downloaded again.