# Query Features in box

This example shows how to Query features in the box on MapView

-   Query features about existing layer id and filter

-   Query features about custom layer id


![Query Features in box](https://static.nextbillion.io/docs-next/docs/maps/android/query-features-in-box.webp)

For all code examples, refer to [Android Maps SDK Code Examples](https://github.com/nextbillion-ai/nb-maps-android-demo)

**activity_query_feature_and_symbol.xml** [view source](https://github.com/nextbillion-ai/nb-maps-android-demo/blob/main/app/src/main/res/layout/activity_query_feature_and_symbol.xml)

```xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ai.nextbillion.maps.core.MapView
        android:id="@+id/mapView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:nbmap_cameraTargetLat="52.0907"
        app:nbmap_cameraTargetLng="5.1214"
        app:nbmap_cameraZoom="16" />

    <FrameLayout
        android:id="@+id/selection_box"
        android:layout_width="150dp"
        android:layout_height="150dp"
        android:layout_centerInParent="true"
        android:alpha="0.3"
        android:background="@color/palette_mint_100" />

</RelativeLayout>
```

**QueryFeatureAndSymbolActivity** [view source](https://github.com/nextbillion-ai/nb-maps-android-demo/blob/main/app/src/main/java/ai/nextbillion/QueryFeatureAndSymbolActivity.java)

```java
package ai.nextbillion;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Color;
import android.graphics.RectF;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import java.io.IOException;
import java.util.List;

import ai.nextbillion.kits.geojson.Feature;
import ai.nextbillion.kits.geojson.FeatureCollection;
import ai.nextbillion.maps.camera.CameraPosition;
import ai.nextbillion.maps.camera.CameraUpdateFactory;
import ai.nextbillion.maps.core.MapView;
import ai.nextbillion.maps.core.NextbillionMap;
import ai.nextbillion.maps.core.Style;
import ai.nextbillion.maps.geometry.LatLng;
import ai.nextbillion.maps.style.expressions.Expression;
import ai.nextbillion.maps.style.layers.FillLayer;
import ai.nextbillion.maps.style.layers.Layer;
import ai.nextbillion.maps.style.layers.SymbolLayer;
import ai.nextbillion.maps.style.sources.GeoJsonSource;
import ai.nextbillion.utils.ResourceUtils;
import androidx.appcompat.app.AppCompatActivity;

import static ai.nextbillion.maps.style.expressions.Expression.get;
import static ai.nextbillion.maps.style.expressions.Expression.literal;
import static ai.nextbillion.maps.style.expressions.Expression.lt;
import static ai.nextbillion.maps.style.expressions.Expression.toNumber;
import static ai.nextbillion.maps.style.layers.PropertyFactory.fillColor;
import static ai.nextbillion.maps.style.layers.PropertyFactory.iconImage;

/**
 * Demo's query rendered features
 */
public class QueryFeatureAndSymbolActivity extends AppCompatActivity {

    public MapView mapView;
    private NextbillionMap nextbillionMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_query_feature_and_symbol);

        final View selectionBox = findViewById(R.id.selection_box);

        // Initialize map as normal
        mapView = (MapView) findViewById(R.id.mapView);
        mapView.onCreate(savedInstanceState);
        mapView.getMapAsync(nextbillionMap -> {
            QueryFeatureAndSymbolActivity.this.nextbillionMap = nextbillionMap;

            CameraPosition position = new CameraPosition.Builder()
                    .target(new LatLng(14.589503119868022, 120.98188196701062))
                    .zoom(16)
                    .bearing(0)
                    .tilt(30)
                    .build();
            nextbillionMap.animateCamera(CameraUpdateFactory.newCameraPosition(position));

            // Add layer / source
            final GeoJsonSource source = new GeoJsonSource("highlighted-shapes-source");
            final Layer layer = new FillLayer("highlighted-shapes-layer", "highlighted-shapes-source")
                    .withProperties(fillColor(Color.YELLOW));

            selectionBox.setOnClickListener(view -> {
                // Query
                int top = selectionBox.getTop() - mapView.getTop();
                int left = selectionBox.getLeft() - mapView.getLeft();
                RectF box = new RectF(left, top, left + selectionBox.getWidth(), top + selectionBox.getHeight());

                Expression filter = lt(toNumber(get("height")), literal(10));
                List<Feature> features = nextbillionMap.queryRenderedFeatures(box, filter, "building");
                List<Feature> symbols = nextbillionMap.queryRenderedFeatures(box, "symbols-layer");

                // Show count
                Toast.makeText(
                        QueryFeatureAndSymbolActivity.this,
                        String.format("%s buildings in box\n%s symbols in box", features.size(), symbols.size()),
                        Toast.LENGTH_SHORT).show();

                // Update source data
                source.setGeoJson(FeatureCollection.fromFeatures(features));
            });

            nextbillionMap.setStyle(new Style.Builder()
                            .fromUri(StyleConstants.NBMAP_STREETS)
                            .withSource(source)
                            .withLayer(layer)
                    , style -> addSymbolLayer(style));

        });
    }

    public void addSymbolLayer(Style style) {
        try {
            String testPoints = ResourceUtils.readRawResource(mapView.getContext(), R.raw.test_points_utrecht);
            Bitmap markerImage = BitmapFactory.decodeResource(getResources(), R.drawable.nbmap_marker_icon_default);

            style.addImage("test-icon", markerImage);
            style.addSource(new GeoJsonSource("symbols-source", testPoints));
            style.addLayer(new SymbolLayer("symbols-layer", "symbols-source")
                    .withProperties(
                            iconImage("test-icon")
                    ));
        } catch (IOException exception) {
            exception.printStackTrace();
        }
    }

    public NextbillionMap getNextbillionMap() {
        return nextbillionMap;
    }

    @Override
    protected void onStart() {
        super.onStart();
        mapView.onStart();
    }

    @Override
    protected void onResume() {
        super.onResume();
        mapView.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mapView.onPause();
    }

    @Override
    protected void onStop() {
        super.onStop();
        mapView.onStop();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        mapView.onSaveInstanceState(outState);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mapView.onDestroy();
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        mapView.onLowMemory();
    }
}
```

The given code is an Android activity that demonstrates how to initialize a MapView, query features on a map, and display the results.

Initializing the MapView:

-   The **onCreate** method initializes the MapView by setting the content view and obtaining a reference to it using findViewById.

-   The onCreate method also calls **mapView.onCreate(savedInstanceState)** to create the **MapView** and **mapView.getMapAsync(this)** to get a reference to the **NextbillionMap** instance when it is ready.


Querying Features of an Existing Layer:

-   The code sets up a map and adds a layer called **"highlighted-shapes-layer"** with a source named **"highlighted-shapes-source"**.

-   The selectionBox view is used to define a rectangular area on the map.

-   When the selectionBox is clicked, the **queryRenderedFeatures** method is called to query the features within the defined **area**.

-   The queried features are **filtered** based on a condition (in this case, the height is less than 10) using an Expression.

-   The queried features are displayed in a toast message.


Querying Features of a Custom Layer:

-   The code adds a custom symbol layer to the map, which is based on a **GeoJSON** source named "symbols-source".

-   The addSymbolLayer method reads **GeoJSON** data from a resource file and adds it as a source and layer to the map style.

-   The **queryRenderedFeatures** method is used to query the features within the defined area for the **"symbols-layer"** specifically.

-   The queried features are displayed in a toast message.


Other Lifecycle Methods: The code also includes various lifecycle methods **(onStart, onResume, onPause, onStop, onSaveInstanceState, onDestroy, onLowMemory)** that should be implemented when using the MapView to properly manage its lifecycle and handle configuration changes.

**Note**: The code uses the Nextbillion Maps SDK and NextbillionMap class to handle map-related operations. It also utilizes the Style class to define the map's visual style, GeoJsonSource class to add data sources, and various layer classes to display map features.