Create a buffer around a map point and display the results as a Graphic.
Use case
Creating buffers is a core concept in GIS proximity analysis that allows you to visualize and locate geographic features contained within a polygon. For example, suppose you wanted to visualize areas of your city where alcohol sales are prohibited because they are within 500 meters of a school. The first step in this proximity analysis would be to generate 500 meter buffer polygons around all schools in the city. Any such businesses you find inside one of the resulting polygons are violating the law.
How to use the sample
Tap on the map. A planar and a geodesic buffer will be created at the tap location using the distance (miles) specified in the text box. Continue tapping to create additional buffers. Notice that buffers closer to the equator appear similar in size. As you move north or south from the equator, however, the geodesic polygons become much larger. Geodesic polygons are in fact a better representation of the true shape and size of the buffer. Geodesic buffers will not be generated for points placed beyond +/-90 degrees latitude. Tap Clear to remove all buffers and start again.
How it works
- The map
Pointfor a tap on the display is captured. - The static method
GeometryEngine.bufferis called to create a planar buffer polygon from the map location and distance. - Another static method,
GeometryEngine.bufferGeodeticis called to create a geodesic buffer polygon using the same inputs. - The polygon results (and tap location) are displayed in the map view with different symbols in order to highlight the difference between the buffer techniques due to the spatial reference used in the planar calculation.
Relevant API
- GeometryEngine.buffer
- GeometryEngine.bufferGeodetic
- GraphicsOverlay
Additional information
Buffers can be generated as either planar (flat - coordinate space of the map's spatial reference) or geodesic (technique that considers the curved shape of the Earth's surface, which is generally a more accurate representation). In general, distortion in the map increases as you move away from the standard parallels of the spatial reference's projection. This map is in Web Mercator so areas near the equator are the most accurate. As you move the buffer location north or south from that line, you'll see a greater difference in the polygon size and shape. Planar operations are generally faster, but performance improvement may only be noticeable for large operations (buffering a great number or complex geometry).
Geodesic buffers in the far northern and southern regions of the map will extend beyond the map's limits. The visible extent of the basemap in this sample is limited to between approximately +/-85 degrees latitude while geodesic buffers are calculated to extend all the way to the poles (+/-90 degrees). Also, since map view wraparound is active, geodesic buffers that cross the international date line (180 degrees longitude) will be normalized, resulting in a multipart geometry. This results in a vertical line in the buffer graphic at the dateline.
For more information about using buffer analysis, see the topic How Buffer (Analysis) works in the ArcGIS Pro documentation.
Tags
analysis, buffer, euclidean, geodesic, geometry, planar
Sample Code
/* Copyright 2022 Esri * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * */ package com.esri.arcgismaps.sample.createplanarandgeodeticbuffers import android.os.Bundle import android.view.View import android.widget.TextView import com.esri.arcgismaps.sample.sampleslib.EdgeToEdgeCompatActivity import androidx.databinding.DataBindingUtil import androidx.lifecycle.lifecycleScope import com.arcgismaps.ApiKey import com.arcgismaps.ArcGISEnvironment import com.arcgismaps.Color import com.arcgismaps.geometry.GeodeticCurveType import com.arcgismaps.geometry.GeometryEngine import com.arcgismaps.geometry.LinearUnit import com.arcgismaps.geometry.LinearUnitId import com.arcgismaps.mapping.ArcGISMap import com.arcgismaps.mapping.BasemapStyle import com.arcgismaps.mapping.symbology.SimpleFillSymbol import com.arcgismaps.mapping.symbology.SimpleFillSymbolStyle import com.arcgismaps.mapping.symbology.SimpleLineSymbol import com.arcgismaps.mapping.symbology.SimpleLineSymbolStyle import com.arcgismaps.mapping.symbology.SimpleMarkerSymbol import com.arcgismaps.mapping.symbology.SimpleMarkerSymbolStyle import com.arcgismaps.mapping.symbology.SimpleRenderer import com.arcgismaps.mapping.view.Graphic import com.arcgismaps.mapping.view.GraphicsOverlay import com.esri.arcgismaps.sample.createplanarandgeodeticbuffers.databinding.CreatePlanarAndGeodeticBuffersActivityMainBinding import com.google.android.material.dialog.MaterialAlertDialogBuilder import com.google.android.material.slider.Slider import kotlinx.coroutines.launch import java.util.Locale class MainActivity : EdgeToEdgeCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) // authentication with an API key or named user is // required to access basemaps and other location services ArcGISEnvironment.apiKey = ApiKey.create(BuildConfig.ACCESS_TOKEN) // set up data binding for the activity val activityMainBinding: CreatePlanarAndGeodeticBuffersActivityMainBinding = DataBindingUtil.setContentView(this, R.layout.create_planar_and_geodetic_buffers_activity_main) // get the views from the layout val mapView = activityMainBinding.mapView val optionsButton = activityMainBinding.optionsButton val clearButton = activityMainBinding.clearButton // add mapview to the lifecycle lifecycle.addObserver(mapView) // create a map with a topographic basemap mapView.map = ArcGISMap(BasemapStyle.ArcGISTopographic) // create a fill symbol for geodesic buffer polygons val geodesicOutlineSymbol = SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.black, 2F) val geodesicBufferFillSymbol = SimpleFillSymbol( SimpleFillSymbolStyle.Solid, Color.green, geodesicOutlineSymbol ) // create a graphics overlay to display geodesic polygons and set its renderer val geodesicGraphicsOverlay = GraphicsOverlay().apply { renderer = SimpleRenderer(geodesicBufferFillSymbol) opacity = 0.5f } // create a fill symbol for planar buffer polygons val planarOutlineSymbol = SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.black, 2F) val planarBufferFillSymbol = SimpleFillSymbol( SimpleFillSymbolStyle.Solid, Color.red, planarOutlineSymbol ) // create a graphics overlay to display planar polygons and set its renderer val planarGraphicsOverlay = GraphicsOverlay().apply { renderer = SimpleRenderer(planarBufferFillSymbol) opacity = 0.5f } // create a marker symbol for tap locations val tapSymbol = SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Cross, Color.white, 14F) // create a graphics overlay to display tap locations for buffers and set its renderer val tapLocationsOverlay = GraphicsOverlay().apply { renderer = SimpleRenderer(tapSymbol) } // add overlays to the mapView mapView.graphicsOverlays.addAll( listOf( geodesicGraphicsOverlay, planarGraphicsOverlay, tapLocationsOverlay ) ) // set the default buffer distance in miles var bufferInMiles = 500f // create a buffer around the clicked location lifecycleScope.launch { mapView.onSingleTapConfirmed.collect { event -> // get map point tapped, return if null val mapPoint = event.mapPoint ?: return@collect // convert the input distance to meters, 1609.34 meters in one mile val bufferInMeters = bufferInMiles * 1609.34 // create a planar buffer graphic around the input location at the specified distance val bufferGeometryPlanar = GeometryEngine.bufferOrNull(mapPoint, bufferInMeters) val planarBufferGraphic = Graphic(bufferGeometryPlanar) // create a geodesic buffer graphic using the same location and distance val bufferGeometryGeodesic = GeometryEngine.bufferGeodeticOrNull( mapPoint, bufferInMeters, LinearUnit(LinearUnitId.Meters), Double.NaN, GeodeticCurveType.Geodesic ) val geodesicBufferGraphic = Graphic(bufferGeometryGeodesic) // create a graphic for the user tap location val locationGraphic = Graphic(mapPoint) // add the buffer polygons and tap location graphics to the appropriate graphic overlays planarGraphicsOverlay.graphics.add(planarBufferGraphic) geodesicGraphicsOverlay.graphics.add(geodesicBufferGraphic) tapLocationsOverlay.graphics.add(locationGraphic) // set button interaction clearButton.isEnabled = true } } // open the option dialog optionsButton.setOnClickListener { val optionsDialog: View = layoutInflater.inflate(R.layout.buffer_options_dialog, null) // set up the dialog builder and the title val dialogBuilder = MaterialAlertDialogBuilder(this) .setView(optionsDialog) .setPositiveButton("Set buffer", null) dialogBuilder.setTitle("Set buffer radius") // set up the dialog views val bufferValue = optionsDialog.findViewById<TextView>(R.id.bufferValue) val bufferSlider = optionsDialog.findViewById<Slider>(R.id.bufferInput) bufferSlider.value = bufferInMiles // set initial buffer text bufferValue.text = String.format(Locale.getDefault(),"%d miles", bufferSlider.value.toInt()) bufferSlider.addOnChangeListener { _, value, _ -> // update buffer text value on slider change bufferValue.text = String.format(Locale.getDefault(),"%d miles", value.toInt()) bufferInMiles = value } // display the dialog dialogBuilder.show() } // clear the graphics from the graphics overlays clearButton.setOnClickListener { planarGraphicsOverlay.graphics.clear() geodesicGraphicsOverlay.graphics.clear() tapLocationsOverlay.graphics.clear() // set button interaction clearButton.isEnabled = false } } }