Custom Map Styles

The HERE SDK for Flutter provides a flexible solution to customize the map by loading custom map schemes.

If you are looking for predefined map styles, see the Quick Start guide for an introduction. The HERE SDK already includes a set of pre-configured map styles such as .normalDay or .satellite.

Create and Load Custom Map Styles

The most flexible solution to customize the map is to create your own map styles using a configuration file generated with the WYSIWYG HERE Style Editor.

As soon as you are satisfied with your custom map style, export it via File -> Export -> Here Rendering Engine Configuration. Please unzip the resulting file. You will find a few JSON files.

Copy all JSON files into the "assets" directory of your project. If not already added, you can add that folder via Android Studio (Right-click on the project: New -> Folder -> Assets folder). You can also manually generate the folder: /your_app/assets. This folder also needs to be included into your pubspec.yaml:

# The following section is specific to Flutter.
flutter:

  # Here we store our custom map styles.
  assets:
    - assets/

The main style file always ends with *.scene.json.

Load the style into a map scene as follows:

import 'dart:io';

import 'package:here_sdk/core.dart';
import 'package:here_sdk/mapview.dart';

...

void loadCustomMapStyle() {
  // From this file other style files can be referenced.
  String filePath = loadCustomStyle('omv-traffic-traffic-normal-night.scene.json');

  // We also need to load referenced style files into the application directory.
  loadCustomStyle('omv-traffic-traffic-normal-night.jss');
  loadCustomStyle('omv-traffic-traffic-normal-night-MapOmvVisibilityRanges.json');
  loadCustomStyle('omv-traffic-traffic-normal-night-layer.properties.json');

  _hereMapController.mapScene.loadSceneFromConfigurationFile(filePath, (MapError? error) {
    if (error == null) {
      // Scene loaded.
    } else {
      print("Map scene not loaded. MapError: " + error.toString());
    }
  });
}

// Retrieves the file from assets folder.
String loadCustomStyle(String assetFile) {
  File file = File("assets/" + assetFile);
  return file.path;
}

With the main *.scene.json file the HERE SDK will find the other referenced style files - as exported from the editor, so we only need to get the file path for this file, but we have to make sure that all style files are kept together at the same folder level.

Using custom map styles can be very effective to differentiate your app from other map applications. In addition, it is possible to change map styles on-the-fly, for example, to shift the user's attention to certain map elements based on the current state of your app.

Load Custom Raster Layers

Another alternative to customize the map's look is to add your own raster tile service on top of the HERE map styles. This can be your own server where you host tiles that you want to show as an overlay on top of selected areas of the world - or a public tile server such as OpenStreetMap. Fully opaque and transparent map tile overlays are supported. It is also possible to add more than one raster layer to the map at the same time.

To add custom raster layers, you need to create a RasterDataSource. A RasterDataSource represents the source of raster tile data to display. It also allows changing its configuration. With a RasterDataSourceConfiguration you can specify a configuration for the data source, including URL, tiling scheme, storage levels and caching parameters.

Finally, with the MapLayerBuilder you can create a MapLayer to add a renderable map overlay to the map.

• Use MapLayerVisibilityRange to specify at which zoom levels the map layer should become visible.
• Use the MapLayerPriority to specify the draw order of the MapLayer.
• Use the MapContentType to specify the type of data to be shown by the MapLayer.

In case of raster tile images, use MapContentType.rasterImage.

Default map gesture actions such as pinch, rotate and zoom behave in the same way for raster tiles as for HERE vector maps - except for a few differences: For example, raster tiles are loaded as bitmaps and therefore a rotated raster map tile rotates all labels and street names contained together with the tile.

Create a RasterDataSource as follows:

RasterDataSource _createRasterDataSource(String dataSourceName) {
  // The URL template that is used to download tiles from the device or a backend data source.
  String templateUrl = "https://stamen-tiles.a.ssl.fastly.net/toner/{z}/{x}/{y}.png";
  // The storage levels available for this data source. Supported range [0, 31].
  List<int> storageLevels = [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
  RasterDataSourceProviderConfiguration rasterProviderConfig =
      RasterDataSourceProviderConfiguration.withDefaults(templateUrl, TilingScheme.quadTreeMercator, storageLevels);

  // Raster tiles are stored in a separate cache on the device.
  String path = "cache/raster/toner";
  int maxDiskSizeInBytes = 1024 * 1024 * 32;
  RasterDataSourceCacheConfiguration cacheConfig = RasterDataSourceCacheConfiguration(path, maxDiskSizeInBytes);

  // Note that this will make the raster source already known to the passed map view.
  return RasterDataSource(_hereMapController.mapContext,
      RasterDataSourceConfiguration.withDefaults(dataSourceName, rasterProviderConfig, cacheConfig));
}

This code uses a tile source from Stamen Design, which can be used under the CC BY 3.0 license. The data itself comes from OpenStreetMap. For more information visit http://maps.stamen.com/#watercolor/12/37.7706/-122.3782.

Note that you can also use other tile sources that follow the OSM standard style format /zoom/x/y.png. The templateURL should look like this:

https://YourRasterTileService.com/{zoom}/{xTile}/{yTile}.png

Here, the zoom value represents the map's current zoom level, and xTile and yTile defines the horizontal and vertical tile numbers.

Once the tile source is created, a MapLayer can be built:

MapLayer _createMapLayer(String dataSourceName) {
  // The layer should be rendered on top of other layers.
  MapLayerPriority priority = MapLayerPriorityBuilder().renderedLast().build();
  // And it should be visible for all zoom levels.
  MapLayerVisibilityRange range = MapLayerVisibilityRange(0, 22 + 1);

  try {
    // Build and add the layer to the map.
    MapLayer mapLayer = MapLayerBuilder()
        .forMap(_hereMapController.hereMapControllerCore) // mandatory parameter
        .withName(dataSourceName + "Layer") // mandatory parameter
        .withDataSource(dataSourceName, MapContentType.rasterImage)
        .withPriority(priority)
        .withVisibilityRange(range)
        .build();
    return mapLayer;
  } on MapLayerBuilderInstantiationException {
    throw Exception("MapLayer creation failed.");
  }
}

And finally, the MapTile's visibility can be controlled by enabling or disabling the layer. Note that we also need to provide a unique name. Each RasterDataSource can be created only once:

String dataSourceName = "myRasterDataSourceTonerStyle";
_rasterDataSourceTonerStyle = _createRasterDataSource(dataSourceName);
_rasterMapLayerTonerStyle = _createMapLayer(dataSourceName);

_rasterMapLayerTonerStyle?.setEnabled(true);

The resulting layer looks like this:

The above screenshot shows that you can easily combine custom raster tiles with other HERE SDK features. For example, you can render several MapMarker instances on top of the tile data from a tile server.

If you do not use an empty base map style, then the underlying map scheme will "shine" through until the raster layer tiles are loaded. The accompanying example app shows how this looks like.

There are certain other parameters that you can adjust: For example, if your app uses multiple raster layers, you can define a load priority when building a layer with the MapLayerBuilder. This allows to specify an integer value: Higher values will lead to load the layer before layers with lower values. Note that this controls just the time when the layer is loaded, the MapLayerPriority controls how the layer is rendered: For example, renderedLast() means that the layer will be rendered on top of all other layers.