Reverse geocode

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Use an online service to find the address for a tapped point.

Image of reverse geocode

Use case

You might use a geocoder to find a customer's delivery address based on the location returned by their device's GPS.

How to use the sample

Tap the map to see the nearest address displayed in a callout.

How it works

  1. Create a LocatorTask object using a URL to a geocoder service.
  2. Set the GeocodeParameters for the LocatorTask and specify the geocoder's attributes.
  3. Get the matching results from the GeocodeResult using LocatorTask.reverseGeocodeAsync.
  4. Show the results using a PictureMarkerSymbol and add the symbol to a Graphic in the GraphicsOverlay.

Additional information

This sample uses the World Geocoding Service. For more information, see the Geocoding service help topic on the ArcGIS Developer website.

Relevant API

  • GeocodeParameters
  • LocatorTask
  • ReverseGeocodeParameters

Tags

address, geocode, locate, reverse geocode, search

Sample Code

ReverseGeocode.cs
                                                                                                                                                                       
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// Copyright 2019 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.

using Android.App;
using Android.OS;
using Android.Widget;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.Tasks.Geocoding;
using Esri.ArcGISRuntime.UI;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using Android.Views;

namespace ArcGISRuntimeXamarin.Samples.ReverseGeocode
{
    [Activity (ConfigurationChanges=Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Reverse geocode",
        category: "Search",
        description: "Use an online service to find the address for a tapped point.",
        instructions: "Tap the map to see the nearest address displayed in a callout.",
        tags: new[] { "address", "geocode", "locate", "reverse geocode", "search" })]
    public class ReverseGeocode : Activity
    {
        // Create and hold reference to the MapView.
        private MapView _myMapView;

        // Service Uri to be provided to the LocatorTask (geocoder).
        private readonly Uri _serviceUri = new Uri("https://geocode-api.arcgis.com/arcgis/rest/services/World/GeocodeServer");

        // The LocatorTask provides geocoding services.
        private LocatorTask _geocoder;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            Title = "Reverse geocode";

            CreateLayout();
            Initialize();
        }

        private async void Initialize()
        {
            // Create new Map with basemap.
            Map myMap = new Map(BasemapStyle.ArcGISImagery);

            // Provide used Map to the MapView.
            _myMapView.Map = myMap;

            // Add a graphics overlay to the map for showing where the user tapped.
            _myMapView.GraphicsOverlays.Add(new GraphicsOverlay());

            // Enable tap-for-info pattern on results.
            _myMapView.GeoViewTapped += _myMapView_GeoViewTapped;

            // Initialize the LocatorTask with the provided service Uri.
            try
            {
                _geocoder = await LocatorTask.CreateAsync(_serviceUri);
            }
            catch (Exception e)
            {
                new AlertDialog.Builder(this).SetMessage(e.ToString()).SetTitle("Error").Show();
            }

            // Set the initial viewpoint.
            await _myMapView.SetViewpointCenterAsync(34.058, -117.195, 5e4);
        }

        private async void _myMapView_GeoViewTapped(object sender, GeoViewInputEventArgs e)
        {
            try
            {
                // Clear the existing graphics & callouts.
                _myMapView.DismissCallout();
                _myMapView.GraphicsOverlays[0].Graphics.Clear();

                // Add a graphic for the tapped point.
                Graphic pinGraphic = await GraphicForPoint(e.Location);
                _myMapView.GraphicsOverlays[0].Graphics.Add(pinGraphic);

                // Normalize the geometry - needed if the user crosses the international date line.
                MapPoint normalizedPoint = (MapPoint)GeometryEngine.NormalizeCentralMeridian(e.Location);

                // Reverse geocode to get addresses.
                IReadOnlyList<GeocodeResult> addresses = await _geocoder.ReverseGeocodeAsync(normalizedPoint);

                // Get the first result.
                GeocodeResult address = addresses.First();

                // Use the city and region for the Callout Title.
                string calloutTitle = address.Attributes["Address"].ToString();

                // Use the metro area for the Callout Detail.
                string calloutDetail = address.Attributes["City"] +
                                       " " + address.Attributes["Region"] +
                                       " " + address.Attributes["CountryCode"];

                // Define the callout.
                CalloutDefinition calloutBody = new CalloutDefinition(calloutTitle, calloutDetail);

                // Show the callout on the map at the tapped location.
                _myMapView.ShowCalloutForGeoElement(pinGraphic, e.Position, calloutBody);
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine(ex);
                new AlertDialog.Builder(this).SetMessage("No results found.").SetTitle("No results").Show();
            }
        }

        private async Task<Graphic> GraphicForPoint(MapPoint point)
        {
            // Get current assembly that contains the image.
            Assembly currentAssembly = Assembly.GetExecutingAssembly();

            // Get image as a stream from the resources.
            // Picture is defined as EmbeddedResource and DoNotCopy.
            Stream resourceStream = currentAssembly.GetManifestResourceStream(
                "ArcGISRuntime.Resources.PictureMarkerSymbols.pin_star_blue.png");

            // Create new symbol using asynchronous factory method from stream.
            PictureMarkerSymbol pinSymbol = await PictureMarkerSymbol.CreateAsync(resourceStream);
            pinSymbol.Width = 60;
            pinSymbol.Height = 60;
            // The image is a pin; offset the image so that the pinpoint.
            //     is on the point rather than the image's true center.
            pinSymbol.LeaderOffsetX = 30;
            pinSymbol.OffsetY = 14;
            return new Graphic(point, pinSymbol);
        }

        private void CreateLayout()
        {
            // Create a new vertical layout for the app.
            var layout = new LinearLayout(this) { Orientation = Orientation.Vertical };

            // Add a help label.
            TextView helpLabel = new TextView(this);
            helpLabel.Text = "Tap to find the nearest address.";
            helpLabel.Gravity = GravityFlags.Center;
            layout.AddView(helpLabel);

            // Add the map view to the layout.
            _myMapView = new MapView(this);
            layout.AddView(_myMapView);

            // Show the layout in the app.
            SetContentView(layout);
        }
    }
}

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