> For the complete documentation index, see [llms.txt](https://docs.mapbox.com/android/maps/llms.txt)

# Within expression

![Usage of the within expression on a buffered geometry.](https://docs.mapbox.com/android/assets/ideal-img/maps-examples-within-expression.d41eaff.480.png)

This example demonstrates the [`within`](https://docs.mapbox.com/style-spec/reference/expressions/#within) expression to filter features outside a specific geometry. The activity sets up a [`MapView`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps/-map-view/) displaying a map with a camera positioned above Washington, D.C. It includes the creation of a buffer around a linestring geometry and the visualization of a route represented by an array of coordinates. Features are filtered using the `within` expression to show only POI labels inside the designated geometry. The app hides various types of labels to emphasize the POI labels on the map.

The activity utilizes classes such as [`SymbolLayer`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.extension.style.layers.generated/-symbol-layer/), [`LineLayer`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.extension.style.layers.generated/-line-layer/), [`FillLayer`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.extension.style.layers.generated/-fill-layer/), and [`MapAnimationOptions`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.plugin.animation/-map-animation-options/), along with methods like [`setCamera`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.plugin.delegates/-map-camera-manager-delegate/set-camera.html) and [`easeTo`](https://docs.mapbox.com/android/maps/api/latest/mapbox-maps-android/com.mapbox.maps.plugin.animation/-camera-animations-plugin/ease-to.html) for map interactions and animations. Customized styling with specific colors, opacities, and visibility settings is applied to enhance the map visualization.

> **Note: Android Examples App Available**
> 
> This example code is part of the **Maps SDK for Android Examples App**, a working Android project [available on GitHub](https://github.com/mapbox/mapbox-maps-android/tree/v11.29.0/). Android developers are encouraged to run the examples app locally to interact with this example in an emulator and explore other features of the Maps SDK.
> 
> See our [Run the Maps SDK for Android Examples App](https://docs.mapbox.com/help/tutorials/maps-sdk-android-examples-app/) tutorial for step-by-step instructions.

**Kotlin**

Title: `WithinExpressionActivity.kt`

[View on GitHub](https://github.com/mapbox/mapbox-maps-android/blob/v11.29.0/app/src/main/java/com/mapbox/maps/testapp/examples/WithinExpressionActivity.kt)

```kt
package com.mapbox.maps.testapp.examples

import android.graphics.Color
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.mapbox.geojson.*
import com.mapbox.maps.CameraOptions
import com.mapbox.maps.MapView
import com.mapbox.maps.Style
import com.mapbox.maps.extension.style.expressions.dsl.generated.within
import com.mapbox.maps.extension.style.layers.addLayerBelow
import com.mapbox.maps.extension.style.layers.generated.SymbolLayer
import com.mapbox.maps.extension.style.layers.generated.fillLayer
import com.mapbox.maps.extension.style.layers.generated.lineLayer
import com.mapbox.maps.extension.style.layers.getLayer
import com.mapbox.maps.extension.style.layers.properties.generated.Visibility
import com.mapbox.maps.extension.style.sources.generated.geoJsonSource
import com.mapbox.maps.extension.style.style
import com.mapbox.maps.plugin.animation.MapAnimationOptions.Companion.mapAnimationOptions
import com.mapbox.maps.plugin.animation.camera

/**
 * An Activity that showcases the within expression to filter features outside a geometry
 */
class WithinExpressionActivity : AppCompatActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val mapView = MapView(this)
    setContentView(mapView)

    val center = Point.fromLngLat(LON, LAT)

    // Setup camera position above Georgetown
    mapView.mapboxMap.setCamera(
      CameraOptions.Builder()
        .center(center)
        .zoom(15.5)
        .build()
    )

    // Assume the route is represented by an array of coordinates.
    val coordinates = listOf<Point>(
      Point.fromLngLat(
        -77.06866264343262,
        38.90506061276737
      ),
      Point.fromLngLat(
        -77.06283688545227,
        38.905194197410545
      ),
      Point.fromLngLat(
        -77.06285834312439,
        38.906429843444094
      ),
      Point.fromLngLat(
        -77.0630407333374,
        38.90680554236621
      )
    )

    // Create buffer around linestring
    val bufferedRouteGeometry = bufferLineStringGeometry()

    mapView.mapboxMap.loadStyle(
      style(Style.MAPBOX_STREETS) {
        +geoJsonSource(POINT_ID) {
          geometry(LineString.fromLngLats(coordinates))
        }
        +geoJsonSource(FILL_ID) {
          featureCollection(FeatureCollection.fromFeature(Feature.fromGeometry(bufferedRouteGeometry)))
          buffer(0)
          tolerance(0.0)
        }
        +layerAtPosition(
          lineLayer(LINE_ID, POINT_ID) {
            lineWidth(7.5)
            lineColor(Color.LTGRAY)
          },
          below = POI_LABEL
        )
      }
    ) { // Add fill layer to represent buffered LineString
      it.addLayerBelow(
        fillLayer(FILL_ID, FILL_ID) {
          fillOpacity(0.12)
          fillColor(Color.YELLOW)
        },
        LINE_ID
      )

      // Move to a new camera position
      mapView.camera.easeTo(
        CameraOptions.Builder()
          .zoom(16.0)
          .center(Point.fromLngLat(-77.06535338052844, 38.905156245642814))
          .bearing(80.68015859462369)
          .pitch(55.0)
          .build(),
        mapAnimationOptions {
          duration(1750)
          startDelay(2000)
        }
      )

      // Show only POI labels inside geometry using within expression
      val symbolLayer = it.getLayer(POI_LABEL) as SymbolLayer
      symbolLayer.filter(within(bufferedRouteGeometry))

      // Hide other types of labels to highlight POI labels
      (it.getLayer(ROAD_LABEL) as SymbolLayer).visibility(
        Visibility.NONE
      )
      (it.getLayer(TRANSIT_LABEL) as SymbolLayer).visibility(
        Visibility.NONE
      )
      (it.getLayer(ROAD_NUMBER_SHIELD) as SymbolLayer).visibility(
        Visibility.NONE
      )
    }
  }

  private fun bufferLineStringGeometry(): Polygon {
    // TODO replace static data by Turf#Buffer: mapbox-java/issues/987
    return FeatureCollection.fromJson(
      """
    {
      "type": "FeatureCollection",
      "features": [
        {
          "type": "Feature",
          "properties": {},
          "geometry": {
            "type": "Polygon",
            "coordinates": [
              [
                [
                  -77.06867337226866,
                  38.90467655551809
                ],
                [
                  -77.06233263015747,
                  38.90479344272695
                ],
                [
                  -77.06234335899353,
                  38.906463238984344
                ],
                [
                  -77.06290125846863,
                  38.907206285691615
                ],
                [
                  -77.06364154815674,
                  38.90684728656818
                ],
                [
                  -77.06326603889465,
                  38.90637140121084
                ],
                [
                  -77.06321239471436,
                  38.905561553883246
                ],
                [
                  -77.0691454410553,
                  38.905436318935635
                ],
                [
                  -77.06912398338318,
                  38.90466820642439
                ],
                [
                  -77.06867337226866,
                  38.90467655551809
                ]
              ]
            ]
          }
        }
      ]
    }
      """.trimIndent()
    ).features()!![0].geometry() as Polygon
  }

  companion object {
    const val POINT_ID = "point"
    const val FILL_ID = "fill"
    const val LINE_ID = "line"
    const val LAT = 38.90628988399711
    const val LON = -77.06574689337494
    const val POI_LABEL = "poi-label"
    const val ROAD_LABEL = "road-label"
    const val TRANSIT_LABEL = "transit-label"
    const val ROAD_NUMBER_SHIELD = "road-number-shield"
  }
}
```