- Introduction
- Add a GeoJsonLayer to your map
- Remove the GeoJsonLayer
- Add and remove a GeoJsonFeature
- Access the GeoJsonFeatures and their properties
- Style the GeoJsonLayer and GeoJsonFeatures
- See the demo app
Introduction
GeoJSON
is an extension of the JSON data
format and represents geographical data. Using this utility, you can store
geographical features in GeoJSON format and render them as a layer on top of
the map. To add and remove your GeoJSON data to and from the map, call addLayerToMap()
and removeLayerFromMap()
respectively. Similarly
you can add and remove individual features by calling addFeature()
and removeFeature()
and passing in a GeoJsonFeature
object. If you want to access the features, you
can call getFeatures()
to get an iterable of all GeoJsonFeature
objects that have been added to the layer.
You can also set default styles to be applied to features before they are
added to the layer, by calling getDefaultPointStyle()
, getDefaultLineStringStyle()
or getDefaultPolygonStyle()
and setting style options on each.
Alternatively, you can set the style for an individual GeoJsonFeature
by calling setPointStyle()
, setLineStringStyle()
or setPolygonStyle()
on the
feature and passing in the relevant style object.
Add a GeoJsonLayer to your map
To add a GeoJson layer to the map, first create an instance of a GeoJsonLayer class. There are two ways to instantiate the GeoJsonLayer.
To import from a JSONObject
, you need the following:
-
GoogleMapobject where the layer is to be rendered -
JSONObjectcontaining the GeoJSON data to be added to the layer
Kotlin
val geoJsonData : JSONObject? = // JSONObject containing the GeoJSON data val layer = GeoJsonLayer ( map , geoJsonData )
Java
JSONObject geoJsonData = // JSONObject containing the GeoJSON data GeoJsonLayer layer = new GeoJsonLayer ( map , geoJsonData );
To import from a local GeoJSON file you need the following:
-
GoogleMapobject where the layer is to be rendered - Local resource file containing the GeoJSON data
-
Contextobject, which is required to open a local resource file
Kotlin
val layer = GeoJsonLayer ( map , R . raw . geojson_file , context )
Java
GeoJsonLayer layer = new GeoJsonLayer ( map , R . raw . geojson_file , context );
After you have created the GeoJsonLayer
, call addLayerToMap()
to add the imported data onto the map:
Kotlin
layer . addLayerToMap ()
Java
layer . addLayerToMap ();
Remove the GeoJsonLayer
Let’s assume that you have added this layer
Kotlin
val geoJsonData : JSONObject? = // JSONObject containing the GeoJSON data val layer = GeoJsonLayer ( map , geoJsonData )
Java
JSONObject geoJsonData = // JSONObject containing the GeoJSON data GeoJsonLayer layer = new GeoJsonLayer ( map , geoJsonData );
To clear the GeoJsonLayer, call removeLayerFromMap()
Kotlin
layer . removeLayerFromMap ()
Java
layer . removeLayerFromMap ();
Add and remove a GeoJsonFeature
A feature in GeoJSON has the type "feature". It contains a geometry, a property member and optionally has a bounding box or an id.
You can create GeoJsonFeature
objects individually, and add them
to the GeoJsonLayer
.
Let's assume that you've created a feature containing a point at 0, 0 with one entry in its properties and no bounding box.
Kotlin
val point = GeoJsonPoint ( LatLng ( 0.0 , 0.0 )) val properties = hashMapOf ( "Ocean" to "South Atlantic" ) val pointFeature = GeoJsonFeature ( point , "Origin" , properties , null )
Java
GeoJsonPoint point = new GeoJsonPoint ( new LatLng ( 0 , 0 )); HashMap<String , String > properties = new HashMap <> (); properties . put ( "Ocean" , "South Atlantic" ); GeoJsonFeature pointFeature = new GeoJsonFeature ( point , "Origin" , properties , null );
To add the feature to the layer, call addFeature()
and pass in
the feature to add.
Kotlin
layer . addFeature ( pointFeature )
Java
layer . addFeature ( pointFeature );
To remove a feature after adding it to the layer, call removeFeature()
and pass in the feature to remove.
Kotlin
layer . removeFeature ( pointFeature )
Java
layer . removeFeature ( pointFeature );
Access the GeoJsonFeatures and their properties
To access all the GeoJsonFeatures that have been added to the layer, you can
call getFeatures()
on the GeoJsonLayer
that you
have created. This will return an iterable of GeoJsonFeatures
that you can access using a for-each loop as shown below.
Kotlin
for ( feature in layer . features ) { // Do something to the feature }
Java
for ( GeoJsonFeature feature : layer . getFeatures ()) { // Do something to the feature }
Use the hasProperty()
and getProperty()
methods in
conjunction with the getFeatures()
method to check if each stored
feature has a particular property and access it if it exists.
Kotlin
if ( feature . hasProperty ( "Ocean" )) { val oceanProperty = feature . getProperty ( "Ocean" ) }
Java
if ( feature . hasProperty ( "Ocean" )) { String oceanProperty = feature . getProperty ( "Ocean" ); }
GeoJSON Geometry Click Events
You can use GeoJsonLayer.OnFeatureClickListener()
to listen for click events on the
geometry features on the map. The following example logs the title of a feature when the user
clicks the feature:
Kotlin
// Set a listener for geometry clicked events. layer . setOnFeatureClickListener { feature - > Log . i ( "GeoJsonClick" , "Feature clicked: ${ feature . getProperty ( " title " ) } " ) }
Java
// Set a listener for geometry clicked events. layer . setOnFeatureClickListener ( new Layer . OnFeatureClickListener () { @Override public void onFeatureClick ( Feature feature ) { Log . i ( "GeoJsonClick" , "Feature clicked: " + feature . getProperty ( "title" )); } });
Style the GeoJsonLayer and GeoJsonFeatures
You can set default styles for a GeoJsonLayer, or style individual features in the layer.
Default Styles
In a GeoJsonLayer, you can set default styles for any points, linestrings and polygons that are added to the layer. Default styles are only applied if the feature does not have a style set for either of its geometries. Any changes you make on the default style will also be reflected in all features that are using the default style.
The steps to apply a default style are as follows
- Retrieve the relevant default style object, this can be one of a
GeoJsonPointStyle, aGeoJsonLineStringStyleor aGeoJsonPolygonStyle. - Apply your desired options on the style.
For example, the following code sample shows how to modify the default point style which will make points draggable with a title and snippet.
Kotlin
val pointStyle = layer . defaultPointStyle pointStyle . isDraggable = true pointStyle . title = "Hello, World!" pointStyle . snippet = "I am a draggable marker"
Java
GeoJsonPointStyle pointStyle = layer . getDefaultPointStyle (); pointStyle . setDraggable ( true ); pointStyle . setTitle ( "Hello, World!" ); pointStyle . setSnippet ( "I am a draggable marker" );
Styles specific to a GeoJsonFeature
Alternatively, you can style individual features in the layer. The steps to
apply a style on a GeoJsonFeature
are as follows.
- Create the relevant style object, this can be either a
GeoJsonPointStyle,GeoJsonLineStringStyleorGeoJsonPolygonStyle. - Apply your desired options on the style.
- Pass the style object to
the relevant method on the
GeoJsonFeature, which will be eithersetPointStyle(),setLineStringStyle()orsetPolygonStyle().
For example, this is how to customise the linestring style for a GeoJsonFeature
so that its color is red.
Kotlin
// Create a new feature containing a linestring val lineStringArray : MutableList<LatLng> = ArrayList () lineStringArray . add ( LatLng ( 0.0 , 0.0 )) lineStringArray . add ( LatLng ( 50.0 , 50.0 )) val lineString = GeoJsonLineString ( lineStringArray ) val lineStringFeature = GeoJsonFeature ( lineString , null , null , null ) // Set the color of the linestring to red val lineStringStyle = GeoJsonLineStringStyle () lineStringStyle . color = Color . RED // Set the style of the feature lineStringFeature . lineStringStyle = lineStringStyle
Java
// Create a new feature containing a linestring List<LatLng> lineStringArray = new ArrayList<LatLng> (); lineStringArray . add ( new LatLng ( 0 , 0 )); lineStringArray . add ( new LatLng ( 50 , 50 )); GeoJsonLineString lineString = new GeoJsonLineString ( lineStringArray ); GeoJsonFeature lineStringFeature = new GeoJsonFeature ( lineString , null , null , null ); // Set the color of the linestring to red GeoJsonLineStringStyle lineStringStyle = new GeoJsonLineStringStyle (); lineStringStyle . setColor ( Color . RED ); // Set the style of the feature lineStringFeature . setLineStringStyle ( lineStringStyle );
See the demo app
For an example of importing a GeoJSON file from a URL and creating a layer
with it, take a look at the GeoJsonDemoActivity
in the demo app
that ships with the utility library. The setup guide
shows you how
to run the demo app.
