Analyze hotspots

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Use a geoprocessing service and a set of features to identify statistically significant hot spots and cold spots.

Image of analyze hotspots

Use case

This tool identifies statistically significant spatial clusters of high values (hot spots) and low values (cold spots). For example, a hotspot analysis based on the frequency of 911 calls within a set region.

How to use the sample

Select a date range (between 1998-01-01 and 1998-05-31) from the dialog and tap on Analyze. The results will be shown on the map upon successful completion of the GeoprocessingJob.

How it works

  1. Create a GeoprocessingTask with the URL set to the endpoint of a geoprocessing service.
  2. Create a query string with the date range as an input of GeoprocessingParameters.
  3. Use the GeoprocessingTask to create a GeoprocessingJob with the GeoprocessingParameters instance.
  4. Start the GeoprocessingJob and wait for it to complete and return a GeoprocessingResult.
  5. Get the resulting ArcGISMapImageLayer using GeoprocessingResult.MapImageLayer.
  6. Add the layer to the map's operational layers.

Relevant API

  • GeoprocessingJob
  • GeoprocessingParameters
  • GeoprocessingResult
  • GeoprocessingTask

Tags

Geoprocessing, GeoprocessingJob, GeoprocessingParameters, GeoprocessingResult

Sample Code

AnalyzeHotspots.cs
                                                                                                                                                                                                                                                                                                                            
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// Copyright 2018 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.Views;
using Android.Widget;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Tasks;
using Esri.ArcGISRuntime.Tasks.Geoprocessing;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Threading.Tasks;

namespace ArcGISRuntime.Samples.AnalyzeHotspots
{
    [Activity (ConfigurationChanges=Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Analyze hotspots",
        category: "Geoprocessing",
        description: "Use a geoprocessing service and a set of features to identify statistically significant hot spots and cold spots.",
        instructions: "Select a date range (between 1998-01-01 and 1998-05-31) from the dialog and tap on Analyze. The results will be shown on the map upon successful completion of the `GeoprocessingJob`.",
        tags: new[] { "Geoprocessing", "GeoprocessingJob", "GeoprocessingParameters", "GeoprocessingResult" })]
    public class AnalyzeHotspots : Activity
    {
        // Hold a reference to the map view.
        private MapView _myMapView;

        // Button to define the start date for the date range.
        private Button _startDateButton;

        // Button to define the end date for the date range.
        private Button _endDateButton;

        // Alert dialog to show when the geoprocessing task is working.
        private AlertDialog _alert;

        // Url for the geoprocessing service.
        private const string _hotspotUrl = "https://sampleserver6.arcgisonline.com/arcgis/rest/services/911CallsHotspot/GPServer/911%20Calls%20Hotspot";

        // The geoprocessing task for hot spot analysis.
        private GeoprocessingTask _hotspotTask;

        // The job that handles the communication between the application and the geoprocessing task.
        private GeoprocessingJob _hotspotJob;

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

            Title = "Analyze Hotspots";

            // Create the UI, setup the control references and execute initialization .
            CreateLayout();
            Initialize();
        }

        private async void Initialize()
        {
            // Create a map with a topographic basemap.
            _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);

            try
            {
                // Create a new geoprocessing task.
                _hotspotTask = await GeoprocessingTask.CreateAsync(new Uri(_hotspotUrl));

                // Zoom into Portland, Oregon.
                await _myMapView.SetViewpointCenterAsync(new MapPoint(-122.66, 45.52, SpatialReferences.Wgs84), 1000000);
            }
            catch (Exception e)
            {
                new AlertDialog.Builder(this).SetMessage(e.ToString()).SetTitle("Error").Show();
            }
        }

        private async void OnRunAnalysisClicked(object sender, EventArgs e)
        {
            // Get the 'from' and 'to' dates from the date edit text's for the geoprocessing analysis.
            DateTime myFromDate;
            DateTime myToDate;

            try
            {
                myFromDate = Convert.ToDateTime(_startDateButton.Text);
                myToDate = Convert.ToDateTime(_endDateButton.Text);
            }
            catch (Exception exception)
            {
                // Show error message and quit.
                new AlertDialog.Builder(this).SetMessage(exception.Message).Show();
                return;
            }

            // Clear any existing results.
            _myMapView.Map.OperationalLayers.Clear();

            // Show busy activity indication.
            _alert.Show();

            // The end date must be at least one day after the start date.
            if (myToDate <= myFromDate.AddDays(1))
            {
                _alert.Cancel();

                // Show error message.
                AlertDialog.Builder alertBuilder = new AlertDialog.Builder(this);
                alertBuilder.SetTitle("Invalid date range");
                alertBuilder.SetMessage("Please select valid time range.There has to be at least one day in between To and From dates.");
                alertBuilder.Show();
                return;
            }

            // Create the parameters that are passed to the used geoprocessing task.
            GeoprocessingParameters myHotspotParameters = new GeoprocessingParameters(GeoprocessingExecutionType.AsynchronousSubmit);

            // Construct the date query.
            string myQueryString = $"(\"DATE\" > date '{myFromDate:yyyy-MM-dd} 00:00:00' AND \"DATE\" < date '{myToDate:yyyy-MM-dd} 00:00:00')";

            // Add the query that contains the date range used in the analysis.
            myHotspotParameters.Inputs.Add("Query", new GeoprocessingString(myQueryString));

            // Create job that handles the communication between the application and the geoprocessing task.
            _hotspotJob = _hotspotTask.CreateJob(myHotspotParameters);
            try
            {
                // Execute the geoprocessing analysis and wait for the results.
                GeoprocessingResult myAnalysisResult = await _hotspotJob.GetResultAsync();

                // Add results to a map using map server from a geoprocessing task.
                // Load to get access to full extent.
                await myAnalysisResult.MapImageLayer.LoadAsync();

                // Add the analysis layer to the map view.
                _myMapView.Map.OperationalLayers.Add(myAnalysisResult.MapImageLayer);

                // Zoom to the results.
                await _myMapView.SetViewpointAsync(new Viewpoint(myAnalysisResult.MapImageLayer.FullExtent));

                // Remove the loading alert dialog.
                _alert.Cancel();
            }
            catch (TaskCanceledException)
            {
                // This is thrown if the task is canceled. Ignore.
            }
            catch (Exception ex)
            {
                // Remove the loading alert dialog.
                _alert.Cancel();

                // Display error messages if the geoprocessing task fails.
                if (_hotspotJob.Status == JobStatus.Failed && _hotspotJob.Error != null)
                {
                    AlertDialog.Builder alertBuilder = new AlertDialog.Builder(this);
                    alertBuilder.SetTitle("Geoprocessing error");
                    alertBuilder.SetMessage("Executing geoprocessing failed. " + _hotspotJob.Error.Message);
                    alertBuilder.Show();
                }
                else
                {
                    AlertDialog.Builder alertBuilder = new AlertDialog.Builder(this);
                    alertBuilder.SetTitle("Sample error");
                    alertBuilder.SetMessage("An error occurred. " + ex.ToString());
                    alertBuilder.Show();
                }
            }
        }

        private void OnDateClicked(object sender, EventArgs a)
        {
            // Get the date from the button text.
            DateTime buttonDate = Convert.ToDateTime(((Button)sender).Text);

            // Create a new DatePickerDialog using the date from the button.
            DatePickerDialog dialog = new DatePickerDialog(this, (EventHandler<DatePickerDialog.DateSetEventArgs>)null, buttonDate.Year, buttonDate.Month - 1, buttonDate.Day);

            // Add an event handler that changes the button text when a date is picked.
            dialog.DateSet += (s, e) => { ((Button)sender).Text = e.Date.ToShortDateString(); };

            // Display the dialog to the user.
            dialog.Show();
        }

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

            LinearLayout.LayoutParams buttonParam = new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.MatchParent,
                ViewGroup.LayoutParams.MatchParent,
                1.0f
            );
            LinearLayout.LayoutParams labelParam = new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.MatchParent,
                ViewGroup.LayoutParams.MatchParent,
                3.0f
            );

            // Create a horizontal sub layout for the start date.
            LinearLayout startDateSubLayout = new LinearLayout(this) { Orientation = Orientation.Horizontal };

            // Label for the start date.
            TextView startDateLabel = new TextView(this)
            {
                Text = "Start Date:",
                LayoutParameters = labelParam,
                Gravity = GravityFlags.Center
            };
            startDateSubLayout.AddView(startDateLabel);

            // Button for the start date.
            _startDateButton = new Button(this)
            {
                Text = "1/01/1998",
                LayoutParameters = buttonParam
            };
            _startDateButton.Click += OnDateClicked;
            startDateSubLayout.AddView(_startDateButton);

            // Add the start date information to the general layout.
            layout.AddView(startDateSubLayout);

            // Create a horizontal sub layout for the end date.
            LinearLayout endDateSubLayout = new LinearLayout(this) { Orientation = Orientation.Horizontal };

            // Label for the end date.
            TextView endDateLabel = new TextView(this)
            {
                Text = "End Date:",
                LayoutParameters = labelParam,
                Gravity = GravityFlags.Center
            };

            endDateSubLayout.AddView(endDateLabel);

            // Button for the end date.
            _endDateButton = new Button(this)
            {
                Text = "1/31/1998",
                LayoutParameters = buttonParam
            };
            _endDateButton.Click += OnDateClicked;
            endDateSubLayout.AddView(_endDateButton);

            // Add the start date information to the general layout.
            layout.AddView(endDateSubLayout);

            // Add a button to the run the hot spot analysis; wire up the click event as well
            Button mapsButton = new Button(this)
            {
                Text = "Run Analysis"
            };
            mapsButton.Click += OnRunAnalysisClicked;
            layout.AddView(mapsButton);

            // Create a layout to be used to alert the user when processing is happening.
            LinearLayout alertLayout = new LinearLayout(this)
            {
                Orientation = Orientation.Vertical
            };

            // Create paramaters for the items in the alert layout.
            LinearLayout.LayoutParams alertParam = new LinearLayout.LayoutParams(
                ViewGroup.LayoutParams.MatchParent,
                ViewGroup.LayoutParams.MatchParent,
                1.0f
            );
            alertParam.SetMargins(0, 10, 0, 10);

            // Text for the processing alert.
            TextView processingText = new TextView(this)
            {
                Text = "Processing...",
                LayoutParameters = alertParam,
                Gravity = GravityFlags.Center,
            };

            // Add the progress bar to indicate the geoprocessing task is running.
            ProgressBar progressBar = new ProgressBar(this)
            {
                Indeterminate = true,
                LayoutParameters = alertParam,
                TextAlignment = TextAlignment.Center
            };

            // Add the text and progress bar to the Linear Layout.
            alertLayout.AddView(processingText);
            alertLayout.AddView(progressBar);

            // Create the alert dialog.
            _alert = new AlertDialog.Builder(this).Create();
            _alert.SetCanceledOnTouchOutside(false);
            _alert.Show();
            _alert.Cancel();

            // Add the layout to the alert.
            _alert.AddContentView(alertLayout, buttonParam);

            // 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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