Polylines and Polygons to Represent Routes and Areas

This tutorial shows you how to add a Google map to your Android app, and use polylines and polygons to represent routes and areas on a map.

Follow the tutorial to build an Android app using the Maps SDK for Android. The recommended development environment is Android Studio.

Get the code

Clone or download the Google Maps Android API v2 Samples repository from GitHub.

Set up your development project

Follow these steps to create the tutorial project in Android Studio.

  1. Download and install Android Studio.
  2. Add the Google Play services package to Android Studio.
  3. Clone or download the Google Maps Android API v2 Samples repository if you didn't do that when you started reading this tutorial.

  4. Import the tutorial project:

    • In Android Studio, select File > New > Import Project.
    • Go to the location where you saved the Google Maps Android API v2 Samples repository after downloading it.
    • Find the Polygons project at this location:
      PATH-TO-SAVED-REPO/android-samples/tutorials/Polygons
    • Select the project directory, then click OK. Android Studio now builds your project, using the Gradle build tool.

Get an API key and enable the necessary APIs

To complete this tutorial, you need a Google API key that's authorized to use the Maps SDK for Android.

Click the button below to get a key and activate the API.

Get Started

For more details, see the full guide to getting an API key.

Add the API key to your app

  1. Edit your project's gradle.properties file.

  2. Paste your API key into the value of the GOOGLE_MAPS_API_KEY property. When you build your app, Gradle copies the API key into the app's Android manifest, as explained below.

    GOOGLE_MAPS_API_KEY=PASTE-YOUR-API-KEY-HERE

Build and run your app

  1. Connect an Android device to your computer. Follow the instructions to enable developer options on your Android device and configure your system to detect the device. (Alternatively, you can use the Android Virtual Device (AVD) Manager to configure a virtual device. When choosing an emulator, make sure you pick an image that includes the Google APIs. For more details, see the getting started guide.)
  2. In Android Studio, click the Run menu option (or the play button icon). Choose a device as prompted.

Android Studio invokes Gradle to build the app, and then runs the app on the device or on the emulator.

You should see a map with two polygons overlaid on top of Australia, similar to the image on this page.

Troubleshooting:

Understand the code

This part of the tutorial explains the most significant parts of the Polygons app, to help you understand how to build a similar app.

Check your Android manifest

Note the following elements in your app's AndroidManifest.xml file:

  • Add a meta-data element to embed the version of Google Play services that the app was compiled with.

    <meta-data
    android:name="com.google.android.gms.version"
    android:value="@integer/google_play_services_version" />

  • Add a meta-data element specifying your API key. The sample accompanying this tutorial maps the value for the API key to a string google_maps_key. When you build your app, Gradle copies the API key from your project's gradle.properties file to the string value.

    <meta-data
  android:name="com.google.android.geo.API_KEY"
  android:value="@string/google_maps_key" />

    To see how the API key maps to the string value, take a look at your app's build.gradle. It contains the following line that maps the string google_maps_key to the gradle property GOOGLE_MAPS_API_KEY:

    resValue "string", "google_maps_key",
        (project.findProperty("GOOGLE_MAPS_API_KEY") ?: "")

Below is a complete example of a manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.polygons">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <meta-data
            android:name="com.google.android.gms.version"
            android:value="@integer/google_play_services_version" />

        <!--
             The API key for Google Maps-based APIs.
        -->
        <meta-data
            android:name="com.google.android.geo.API_KEY"
            android:value="@string/google_maps_key" />

        <activity
            android:name="com.example.polygons.PolyActivity"
            android:label="@string/title_activity_maps">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

Add a map

Display a map, using the Maps SDK for Android.

  1. Add a <fragment> element to your activity's layout file, activity_maps.xml. This element defines a SupportMapFragment to act as a container for the map and to provide access to the GoogleMap object. The tutorial uses the Android support library version of the map fragment, to ensure backward compatibility with earlier versions of the Android framework.

    <fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.polygons.PolyActivity" />

  2. In your activity's onCreate() method, set the layout file as the content view. Get a handle to the map fragment by calling FragmentManager.findFragmentById(). Then use getMapAsync() to register for the map callback:

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Retrieve the content view that renders the map.
    setContentView(R.layout.activity_maps);

    // Get the SupportMapFragment and request notification when the map is ready to be used.
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(map);
    mapFragment.getMapAsync(this);
}

  3. Implement the OnMapReadyCallback interface and override the onMapReady() method. The API invokes this callback when the GoogleMap object is available, so you can add objects to the map and further customize it for your app:

    public class PolyActivity extends AppCompatActivity
        implements
                OnMapReadyCallback,
                GoogleMap.OnPolylineClickListener,
                GoogleMap.OnPolygonClickListener {

    // More code goes here, including the onCreate() method described above.

    @Override
    public void onMapReady(GoogleMap googleMap) {

        // Add polylines and polygons to the map. This section shows just
        // a single polyline. Read the rest of the tutorial to learn more.
        Polyline polyline1 = googleMap.addPolyline(new PolylineOptions()
                .clickable(true)
                .add(
                        new LatLng(-35.016, 143.321),
                        new LatLng(-34.747, 145.592),
                        new LatLng(-34.364, 147.891),
                        new LatLng(-33.501, 150.217),
                        new LatLng(-32.306, 149.248),
                        new LatLng(-32.491, 147.309)));

        // Position the map's camera near Alice Springs in the center of Australia,
        // and set the zoom factor so most of Australia shows on the screen.
        googleMap.moveCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(-23.684, 133.903), 4));

        // Set listeners for click events.
        googleMap.setOnPolylineClickListener(this);
        googleMap.setOnPolygonClickListener(this);
    }
}

Add a polyline to draw a line on the map

A Polyline is a series of connected line segments. Polylines are useful to represent routes, paths, or other connections between locations on the map.

  1. Create a PolylineOptions object and add points to it. Each point represents a location on the map, which you define with a LatLng object containing latitude and longitude values. The code sample below creates a polyline with 6 points.

  2. Call GoogleMap.addPolyline() to add the polyline to the map.

    Polyline polyline1 = googleMap.addPolyline(new PolylineOptions()
        .clickable(true)
        .add(
                new LatLng(-35.016, 143.321),
                new LatLng(-34.747, 145.592),
                new LatLng(-34.364, 147.891),
                new LatLng(-33.501, 150.217),
                new LatLng(-32.306, 149.248),
                new LatLng(-32.491, 147.309)));

Set the polyline's clickable option to true if you want to handle click events on the polyline. There's more about event handling later in this tutorial.

Store arbitrary data with a polyline

You can store arbitrary data objects with polylines and other geometry objects.

  1. Call Polyline.setTag() to store a data object with the polyline. The code below defines an arbitrary tag (A) indicating a type of polyline.

    Polyline polyline1 = googleMap.addPolyline(new PolylineOptions()
        .clickable(true)
        .add(
                new LatLng(-35.016, 143.321),
                new LatLng(-34.747, 145.592),
                new LatLng(-34.364, 147.891),
                new LatLng(-33.501, 150.217),
                new LatLng(-32.306, 149.248),
                new LatLng(-32.491, 147.309)));
// Store a data object with the polyline, used here to indicate an arbitrary type.
polyline1.setTag("A");

  2. Retrieve the data using Polyline.getTag(), as the next section shows.

Add custom styling to your polyline

You can specify various styling properties in the PolylineOptions object. Styling options include the stroke color, stroke width, stroke pattern, joint types, and start and end caps. If you don't specify a particular property, the API uses a default for that property.

The following code applies a round cap to the end of the line, and a different start cap depending on the polyline's type, where the type is an arbitrary property stored in the data object for the polyline. The sample also specifies a stroke width, stroke color, and joint type:

private static final int COLOR_BLACK_ARGB = 0xff000000;
private static final int POLYLINE_STROKE_WIDTH_PX = 12;

private void stylePolyline(Polyline polyline) {
    String type = "";
    // Get the data object stored with the polyline.
    if (polyline.getTag() != null) {
        type = polyline.getTag().toString();
    }

    switch (type) {
        // If no type is given, allow the API to use the default.
        case "A":
            // Use a custom bitmap as the cap at the start of the line.
            polyline.setStartCap(
                    new CustomCap(
                            BitmapDescriptorFactory.fromResource(R.drawable.ic_arrow), 10));
            break;
        case "B":
            // Use a round cap at the start of the line.
            polyline.setStartCap(new RoundCap());
            break;
    }

    polyline.setEndCap(new RoundCap());
    polyline.setWidth(POLYLINE_STROKE_WIDTH_PX);
    polyline.setColor(COLOR_BLACK_ARGB);
    polyline.setJointType(JointType.ROUND);
}

The above code specifies a custom bitmap for the start cap of the type A polyline, and specifies a reference stroke width of 10 pixels. The API scales the bitmap based on the reference stroke width. When specifying the reference stroke width, supply the width that you used when designing the bitmap image, at the original dimension of the image. Hint: Open your bitmap image at 100% zoom in an image editor, and plot the desired width of the line stroke relative to the image.

Read more about line caps and other options for customizing shapes.

Handle click events on the polyline

  1. Make the polyline clickable by calling Polyline.setClickable(). (By default, polylines are not clickable and your app will not receive a notification when the user taps a polyline.)

  2. Implement the OnPolylineClickListener interface and call GoogleMap.setOnPolylineClickListener() to set the listener on the map:

    public class PolyActivity extends AppCompatActivity
        implements
                OnMapReadyCallback,
                GoogleMap.OnPolylineClickListener,
                GoogleMap.OnPolygonClickListener {

    @Override
    public void onMapReady(GoogleMap googleMap) {
        // Add a polyline to the map.
        Polyline polyline1 = googleMap.addPolyline((new PolylineOptions())
                .clickable(true)
                .add(new LatLng(-35.016, 143.321),
                        new LatLng(-34.747, 145.592),
                        new LatLng(-34.364, 147.891),
                        new LatLng(-33.501, 150.217),
                        new LatLng(-32.306, 149.248),
                        new LatLng(-32.491, 147.309)));

        // Set listeners for click events.
        googleMap.setOnPolylineClickListener(this);
        googleMap.setOnPolygonClickListener(this);
    }
}

  3. Override the onPolylineClick() callback method. The following example alternates the stroke pattern of the line between solid and dotted, each time the user clicks the polyline:

    private static final PatternItem DOT = new Dot();
private static final PatternItem GAP = new Gap(PATTERN_GAP_LENGTH_PX);
//
// Create a stroke pattern of a gap followed by a dot.
private static final List<PatternItem> PATTERN_POLYLINE_DOTTED = Arrays.asList(GAP, DOT);

@Override
public void onPolylineClick(Polyline polyline) {
    // Flip from solid stroke to dotted stroke pattern.
    if ((polyline.getPattern() == null) || (!polyline.getPattern().contains(DOT))) {
        polyline.setPattern(PATTERN_POLYLINE_DOTTED);
    } else {
        // The default pattern is a solid stroke.
        polyline.setPattern(null);
    }

    Toast.makeText(this, "Route type " + polyline.getTag().toString(),
            Toast.LENGTH_SHORT).show();
}

Add polygons to represent areas on the map

A Polygon is a shape consisting of a series of coordinates in an ordered sequence, similar to a Polyline. The difference is that polygon defines a closed area with a fillable interior, while a polyline is open ended.

  1. Create a PolygonOptions object and add points to it. Each point represents a location on the map, which you define with a LatLng object containing latitude and longitude values. The code sample below creates a polygon with 4 points.

  2. Make the polygon clickable by calling Polygon.setClickable(). (By default, polygons are not clickable and your app will not receive a notification when the user taps a polygon.) Handling polygon click events is similar to handling the events on polylines, described earlier in this tutorial.

  3. Call GoogleMap.addPolygon() to add the polygon to the map.

  4. Call Polygon.setTag() to store a data object with the polygon. The code below defines an arbitrary type (alpha) for the polygon.

    Polygon polygon1 = googleMap.addPolygon(new PolygonOptions()
        .clickable(true)
        .add(
                new LatLng(-27.457, 153.040),
                new LatLng(-33.852, 151.211),
                new LatLng(-37.813, 144.962),
                new LatLng(-34.928, 138.599)));
// Store a data object with the polygon, used here to indicate an arbitrary type.
polygon1.setTag("alpha");

Add custom styling to your polygon

You can specify a number of styling properties in the PolygonOptions object. Styling options include the stroke color, stroke width, stroke pattern, stroke joint types, and fill color. If you don't specify a particular property, the API uses a default for that property.

The following code applies specific colors and stroke patterns depending on the polygon's type, where the type is an arbitrary property stored in the data object for the polygon:

private static final int COLOR_BLACK_ARGB = 0xff000000;
private static final int COLOR_WHITE_ARGB = 0xffffffff;
private static final int COLOR_GREEN_ARGB = 0xff388E3C;
private static final int COLOR_PURPLE_ARGB = 0xff81C784;
private static final int COLOR_ORANGE_ARGB = 0xffF57F17;
private static final int COLOR_BLUE_ARGB = 0xffF9A825;

private static final int POLYGON_STROKE_WIDTH_PX = 8;
private static final int PATTERN_DASH_LENGTH_PX = 20;
private static final int PATTERN_GAP_LENGTH_PX = 20;
private static final PatternItem DOT = new Dot();
private static final PatternItem DASH = new Dash(PATTERN_DASH_LENGTH_PX);
private static final PatternItem GAP = new Gap(PATTERN_GAP_LENGTH_PX);

// Create a stroke pattern of a gap followed by a dash.
private static final List<PatternItem> PATTERN_POLYGON_ALPHA = Arrays.asList(GAP, DASH);

// Create a stroke pattern of a dot followed by a gap, a dash, and another gap.
private static final List<PatternItem> PATTERN_POLYGON_BETA =
        Arrays.asList(DOT, GAP, DASH, GAP);

private void stylePolygon(Polygon polygon) {
    String type = "";
    // Get the data object stored with the polygon.
    if (polygon.getTag() != null) {
        type = polygon.getTag().toString();
    }

    List<PatternItem> pattern = null;
    int strokeColor = COLOR_BLACK_ARGB;
    int fillColor = COLOR_WHITE_ARGB;

    switch (type) {
        // If no type is given, allow the API to use the default.
        case "alpha":
            // Apply a stroke pattern to render a dashed line, and define colors.
            pattern = PATTERN_POLYGON_ALPHA;
            strokeColor = COLOR_GREEN_ARGB;
            fillColor = COLOR_PURPLE_ARGB;
            break;
        case "beta":
            // Apply a stroke pattern to render a line of dots and dashes, and define colors.
            pattern = PATTERN_POLYGON_BETA;
            strokeColor = COLOR_ORANGE_ARGB;
            fillColor = COLOR_BLUE_ARGB;
            break;
    }

    polygon.setStrokePattern(pattern);
    polygon.setStrokeWidth(POLYGON_STROKE_WIDTH_PX);
    polygon.setStrokeColor(strokeColor);
    polygon.setFillColor(fillColor);
}

Read more about stroke patterns and other options for customizing shapes.

Next steps

Learn about the Circle object. Circles are similar to polygons but have properties that reflect the shape of a circle.