Worked on interface

packages/google_maps_flutter/google_maps_flutter/example/lib/heatmap_layer.dart

@@ -0,0 +1,120 @@
+// ignore_for_file: public_member_api_docs
+
+import 'package:flutter/material.dart';
+import 'package:google_maps_flutter/google_maps_flutter.dart';
+import 'package:google_maps_flutter_example/page.dart';
+
+class HeatmapLayerPage extends GoogleMapExampleAppPage {
+  const HeatmapLayerPage() : super(const Icon(Icons.map), 'Heatmap layer');
+
+  @override
+  Widget build(BuildContext context) {
+    return const HeatmapLayerBody();
+  }
+}
+
+class HeatmapLayerBody extends StatefulWidget {
+  const HeatmapLayerBody();
+
+  @override
+  State<StatefulWidget> createState() => HeatmapLayerBodyState();
+}
+
+class HeatmapLayerBodyState extends State<HeatmapLayerBody> {
+  static const LatLng sanFrancisco = LatLng(37.774546, -122.433523);
+
+  List<WeightedLatLng> disabledPoints = <WeightedLatLng>[
+    WeightedLatLng(37.782, -122.447),
+    WeightedLatLng(37.782, -122.445),
+    WeightedLatLng(37.782, -122.443),
+    WeightedLatLng(37.782, -122.441),
+    WeightedLatLng(37.782, -122.439),
+    WeightedLatLng(37.782, -122.437),
+    WeightedLatLng(37.782, -122.435),
+    WeightedLatLng(37.785, -122.447),
+    WeightedLatLng(37.785, -122.445),
+    WeightedLatLng(37.785, -122.443),
+    WeightedLatLng(37.785, -122.441),
+    WeightedLatLng(37.785, -122.439),
+    WeightedLatLng(37.785, -122.437),
+    WeightedLatLng(37.785, -122.435)
+  ];
+
+  List<WeightedLatLng> enabledPoints = <WeightedLatLng>[];
+
+  void _addPoint() {
+    if (disabledPoints.isEmpty) {
+      return;
+    }
+
+    final WeightedLatLng point = disabledPoints.first;
+    disabledPoints.removeAt(0);
+
+    setState(() => enabledPoints.add(point));
+  }
+
+  void _removePoint() {
+    if (enabledPoints.isEmpty) {
+      return;
+    }
+
+    final WeightedLatLng point = enabledPoints.first;
+    enabledPoints.removeAt(0);
+
+    setState(() => disabledPoints.add(point));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      children: <Widget>[
+        Center(
+          child: SizedBox(
+            width: 350.0,
+            height: 300.0,
+            child: GoogleMap(
+                initialCameraPosition: const CameraPosition(
+                  target: sanFrancisco,
+                  zoom: 13,
+                ),
+                heatmapLayers: <HeatmapLayer>{
+                  HeatmapLayer(
+                    heatmapLayerId: const HeatmapLayerId('test'),
+                    data: enabledPoints,
+                  )
+                }),
+          ),
+        ),
+        Expanded(
+          child: SingleChildScrollView(
+            child: Row(
+              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+              children: <Widget>[
+                Row(
+                  children: <Widget>[
+                    Column(
+                      children: <Widget>[
+                        TextButton(
+                          child: const Text('Add point'),
+                          onPressed:
+                              disabledPoints.isNotEmpty ? _addPoint : null,
+                        ),
+                        TextButton(
+                          child: const Text('Remove point'),
+                          onPressed:
+                              enabledPoints.isNotEmpty ? _removePoint : null,
+                        ),
+                      ],
+                    )
+                  ],
+                )
+              ],
+            ),
+          ),
+        ),
+      ],
+    );
+  }
+}

packages/google_maps_flutter/google_maps_flutter/example/lib/main.dart

@@ -10,6 +10,7 @@ import 'package:flutter/material.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';
 import 'package:google_maps_flutter_example/lite_mode.dart';
 import 'animate_camera.dart';
+import 'heatmap_layer.dart';
 import 'map_click.dart';
 import 'map_coordinates.dart';
 import 'map_ui.dart';
@@ -41,6 +42,7 @@ final List<GoogleMapExampleAppPage> _allPages = <GoogleMapExampleAppPage>[
   const SnapshotPage(),
   const LiteModePage(),
   const TileOverlayPage(),
+  const HeatmapLayerPage(),
 ];
 
 class MapsDemo extends StatelessWidget {

packages/google_maps_flutter/google_maps_flutter/lib/google_maps_flutter.dart

@@ -27,10 +27,13 @@ export 'package:google_maps_flutter_platform_interface/google_maps_flutter_platf
         Cap,
         Circle,
         CircleId,
+        HeatmapLayer,
+        HeatmapLayerId,
         InfoWindow,
         JointType,
         LatLng,
         LatLngBounds,
+        WeightedLatLng,
         MapStyleException,
         MapType,
         Marker,

packages/google_maps_flutter/google_maps_flutter/lib/src/controller.dart

@@ -154,6 +154,18 @@ class GoogleMapController {
         .updateCircles(circleUpdates, mapId: mapId);
   }
 
+  /// Updates heatmap layer configuration.
+  ///
+  /// Change listeners are notified once the update has been made on the
+  /// platform side.
+  ///
+  /// The returned [Future] completes after listeners have been notified.
+  Future<void> _updateHeatmapLayers(HeatmapLayerUpdates heatmapLayerUpdates) {
+    assert(heatmapLayerUpdates != null);
+    return GoogleMapsFlutterPlatform.instance
+        .updateHeatmapLayers(heatmapLayerUpdates, mapId: mapId);
+  }
+
   /// Updates tile overlays configuration.
   ///
   /// Change listeners are notified once the update has been made on the

packages/google_maps_flutter/google_maps_flutter/lib/src/google_map.dart

@@ -113,6 +113,7 @@ class GoogleMap extends StatefulWidget {
     this.polygons = const <Polygon>{},
     this.polylines = const <Polyline>{},
     this.circles = const <Circle>{},
+    this.heatmapLayers = const <HeatmapLayer>{},
     this.onCameraMoveStarted,
     this.tileOverlays = const <TileOverlay>{},
     this.onCameraMove,
@@ -191,6 +192,9 @@ class GoogleMap extends StatefulWidget {
   /// Circles to be placed on the map.
   final Set<Circle> circles;
 
+  /// Heatmap layers to show on the map.
+  final Set<HeatmapLayer> heatmapLayers;
+
   /// Tile overlays to be placed on the map.
   final Set<TileOverlay> tileOverlays;
 
@@ -294,6 +298,8 @@ class _GoogleMapState extends State<GoogleMap> {
   Map<PolygonId, Polygon> _polygons = <PolygonId, Polygon>{};
   Map<PolylineId, Polyline> _polylines = <PolylineId, Polyline>{};
   Map<CircleId, Circle> _circles = <CircleId, Circle>{};
+  Map<HeatmapLayerId, HeatmapLayer> _heatmapLayers =
+      <HeatmapLayerId, HeatmapLayer>{};
   late _GoogleMapOptions _googleMapOptions;
 
   @override
@@ -309,6 +315,7 @@ class _GoogleMapState extends State<GoogleMap> {
       polygons: widget.polygons,
       polylines: widget.polylines,
       circles: widget.circles,
+      heatmapLayers: widget.heatmapLayers,
       gestureRecognizers: widget.gestureRecognizers,
       mapOptions: _googleMapOptions.toMap(),
     );
@@ -322,6 +329,7 @@ class _GoogleMapState extends State<GoogleMap> {
     _polygons = keyByPolygonId(widget.polygons);
     _polylines = keyByPolylineId(widget.polylines);
     _circles = keyByCircleId(widget.circles);
+    _heatmapLayers = keyByHeatmapLayerId(widget.heatmapLayers);
   }
 
   @override
@@ -343,6 +351,7 @@ class _GoogleMapState extends State<GoogleMap> {
     _updatePolygons();
     _updatePolylines();
     _updateCircles();
+    _updateHeatmapLayers();
     _updateTileOverlays();
   }
 
@@ -391,6 +400,16 @@ class _GoogleMapState extends State<GoogleMap> {
     _circles = keyByCircleId(widget.circles);
   }
 
+  Future<void> _updateHeatmapLayers() async {
+    final GoogleMapController controller = await _controller.future;
+    // ignore: unawaited_futures
+    controller._updateHeatmapLayers(
+      HeatmapLayerUpdates.from(
+          _heatmapLayers.values.toSet(), widget.heatmapLayers),
+    );
+    _heatmapLayers = keyByHeatmapLayerId(widget.heatmapLayers);
+  }
+
   Future<void> _updateTileOverlays() async {
     final GoogleMapController controller = await _controller.future;
     // ignore: unawaited_futures

packages/google_maps_flutter/google_maps_flutter/test/fake_maps_controllers.dart

@@ -4,6 +4,7 @@
 
 import 'dart:typed_data';
 
+import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';
@@ -20,6 +21,7 @@ class FakePlatformGoogleMap {
     updatePolygons(params);
     updatePolylines(params);
     updateCircles(params);
+    updateHeatmapLayers(params);
     updateTileOverlays(Map.castFrom<dynamic, dynamic, String, dynamic>(params));
   }
 
@@ -85,6 +87,12 @@ class FakePlatformGoogleMap {
 
   Set<Circle> circlesToChange = <Circle>{};
 
+  Set<HeatmapLayerId> heatmapLayerIdsToRemove = <HeatmapLayerId>{};
+
+  Set<HeatmapLayer> heatmapLayersToAdd = <HeatmapLayer>{};
+
+  Set<HeatmapLayer> heatmapLayersToChange = <HeatmapLayer>{};
+
   Set<TileOverlayId> tileOverlayIdsToRemove = <TileOverlayId>{};
 
   Set<TileOverlay> tileOverlaysToAdd = <TileOverlay>{};
@@ -112,6 +120,9 @@ class FakePlatformGoogleMap {
       case 'circles#update':
         updateCircles(call.arguments as Map<dynamic, dynamic>?);
         return Future<void>.sync(() {});
+      case 'heatmapLayers#update':
+        updateHeatmapLayers(call.arguments as Map<dynamic, dynamic>?);
+        return Future<void>.sync(() {});
       default:
         return Future<void>.sync(() {});
     }
@@ -288,6 +299,18 @@ class FakePlatformGoogleMap {
     circlesToChange = _deserializeCircles(circleUpdates['circlesToChange']);
   }
 
+  void updateHeatmapLayers(Map<dynamic, dynamic>? heatmapLayerUpdates) {
+    if (heatmapLayerUpdates == null) {
+      return;
+    }
+    heatmapLayersToAdd =
+        _deserializeHeatmapLayers(heatmapLayerUpdates['heatmapLayersToAdd']);
+    heatmapLayerIdsToRemove = _deserializeHeatmapLayerIds(
+        heatmapLayerUpdates['heatmapLayerIdsToRemove'] as List<dynamic>?);
+    heatmapLayersToChange =
+        _deserializeHeatmapLayers(heatmapLayerUpdates['heatmapLayersToChange']);
+  }
+
   void updateTileOverlays(Map<String, dynamic> updateTileOverlayUpdates) {
     if (updateTileOverlayUpdates == null) {
       return;
@@ -346,6 +369,58 @@ class FakePlatformGoogleMap {
     return result;
   }
 
+  Set<HeatmapLayerId> _deserializeHeatmapLayerIds(
+      List<dynamic>? heatmapLayerIds) {
+    if (heatmapLayerIds == null) {
+      return <HeatmapLayerId>{};
+    }
+    return heatmapLayerIds
+        .map(
+          (dynamic heatmapLayerId) => HeatmapLayerId(heatmapLayerId as String),
+        )
+        .toSet();
+  }
+
+  Set<HeatmapLayer> _deserializeHeatmapLayers(dynamic heatmapLayers) {
+    if (heatmapLayers == null) {
+      return <HeatmapLayer>{};
+    }
+    final List<dynamic> heatmapLayersData = heatmapLayers as List<dynamic>;
+    final Set<HeatmapLayer> result = <HeatmapLayer>{};
+    for (final Map<dynamic, dynamic> heatmapLayerData
+        in heatmapLayersData.cast<Map<dynamic, dynamic>>()) {
+      final String heatmapLayerId =
+          heatmapLayerData['heatmapLayerId'] as String;
+
+      final List<dynamic> dataData = heatmapLayerData['data'] as List<dynamic>;
+      final List<WeightedLatLng> data =
+          dataData.map((dynamic e) => WeightedLatLng.fromJson(e)!).toList();
+
+      final bool dissipating = heatmapLayerData['dissipating'] as bool;
+
+      final List<dynamic>? gradientData =
+          heatmapLayerData['gradient'] as List<dynamic>?;
+      final List<Color>? gradient =
+          gradientData?.cast<int>().map((int e) => Color(e)).toList();
+
+      final double? maxIntensity = heatmapLayerData['maxIntensity'] as double?;
+      final double opacity = heatmapLayerData['opacity'] as double;
+      final double? radius = heatmapLayerData['radius'] as double?;
+
+      result.add(HeatmapLayer(
+        heatmapLayerId: HeatmapLayerId(heatmapLayerId),
+        data: data,
+        dissipating: dissipating,
+        gradient: gradient,
+        maxIntensity: maxIntensity,
+        opacity: opacity,
+        radius: radius,
+      ));
+    }
+
+    return result;
+  }
+
   Set<TileOverlayId> _deserializeTileOverlayIds(List<String>? tileOverlayIds) {
     if (tileOverlayIds == null || tileOverlayIds.isEmpty) {
       return <TileOverlayId>{};

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/heatmap_layer.dart

@@ -86,7 +86,10 @@ class HeatmapLayer implements MapsObject<HeatmapLayer> {
 
   /// Creates a new [HeatmapLayer] object whose values are the same as this
   /// instance.
-  HeatmapLayer clone() => copyWith();
+  HeatmapLayer clone() => copyWith(
+        dataParam: List.of(data),
+        gradientParam: gradient != null ? List.of(gradient!) : null,
+      );
 
   /// Converts this object to something serializable in JSON.
   Object toJson() {

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/location.dart

@@ -143,7 +143,8 @@ class WeightedLatLng {
   final double weight;
 
   /// Creates a [WeightedLatLng] with the specified [weight]
-  WeightedLatLng(this.location, {this.weight = 1.0});
+  WeightedLatLng(double latitude, double longitude, {this.weight = 1.0})
+      : location = LatLng(latitude, longitude);
 
   /// Converts this object to something serializable in JSON.
   Object toJson() {
@@ -157,8 +158,10 @@ class WeightedLatLng {
     }
     assert(json is List && json.length == 2);
     final list = json as List;
+    final latLng = LatLng.fromJson(list[0])!;
     return WeightedLatLng(
-      LatLng.fromJson(list[0])!,
+      latLng.latitude,
+      latLng.longitude,
       weight: list[1],
     );
   }

packages/google_maps_flutter/google_maps_flutter_web/README.md

@@ -26,6 +26,8 @@ Modify the `<head>` tag of your `web/index.html` to load the Google Maps JavaScr
 
 Now you should be able to use the Google Maps plugin normally.
 
+To use heatmap layers, add `&libraries=visualization` to the end of the URL.
+
 ## Limitations of the web version
 
 The following map options are not available in web, because the map doesn't rotate there: