Distance Expression | Maps SDK | Android Docs

Show POIs on a map with distance expression filter.

Android Examples App Available

This example code is part of the Maps SDK for Android Examples App, a working Android project available on GitHub. 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 tutorial for step-by-step instructions.

Kotlin

DistanceExpressionActivity.kt

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package com.mapbox.maps.testapp.examples

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.mapbox.geojson.Point
import com.mapbox.maps.CameraOptions
import com.mapbox.maps.MapView
import com.mapbox.maps.Style
import com.mapbox.maps.extension.style.expressions.dsl.generated.lt
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.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.turf.TurfConstants
import com.mapbox.turf.TurfTransformation

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

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

    val center = Point.fromLngLat(LON, LAT)
    val circle = TurfTransformation.circle(center, RADIUS, TurfConstants.UNIT_METERS)

    // Setup camera position above Georgetown
    mapView.mapboxMap.setCamera(CameraOptions.Builder().center(center).zoom(16.0).build())

    mapView.mapboxMap.loadStyle(
      style(Style.MAPBOX_STREETS) {
        +geoJsonSource(POINT_ID) {
          geometry(center)
        }
        +geoJsonSource(CIRCLE_ID) {
          geometry(circle)
        }
        +layerAtPosition(
          fillLayer(CIRCLE_ID, CIRCLE_ID) {
            fillOpacity(0.5)
            fillColor("#3bb2d0")
          },
          below = POI_LABEL
        )
      }
    ) {
      val symbolLayer = it.getLayer("poi-label") as SymbolLayer
      symbolLayer.filter(
        lt {
          distance(Point.fromLngLat(LON, LAT))
          literal(150)
        }
      )
      // 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)
    }
  }

  companion object {
    const val POINT_ID = "point"
    const val CIRCLE_ID = "circle"
    const val LAT = 37.78794572301525
    const val LON = -122.40752220153807
    const val RADIUS = 150.0
    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"
  }
}

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