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.csDateSelectionViewController.cs
                                                                                                                                                                                                                                          
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// Copyright 2017 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 System;
using System.Threading.Tasks;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Tasks;
using Esri.ArcGISRuntime.Tasks.Geoprocessing;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using UIKit;

namespace ArcGISRuntime.Samples.AnalyzeHotspots
{
    [Register("AnalyzeHotspots")]
    [ArcGISRuntime.Samples.Shared.Attributes.ClassFile("DateSelectionViewController.cs")]
    [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 : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIBarButtonItem _configureButton;
        private UIBarButtonItem _startButton;
        private DateSelectionViewController _selectionView;
        private UIActivityIndicatorView _progressBar;

        // 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 spots analysis.
        private GeoprocessingTask _hotspotTask;

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

        public AnalyzeHotspots()
        {
            Title = "Analyze hotspots";
        }

        private async void Initialize()
        {
            // Create and show 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));
            }
            catch (Exception e)
            {
                new UIAlertView("Error", e.ToString(), (IUIAlertViewDelegate) null, "OK", null).Show();
            }
        }

        private async void OnRunAnalysisClicked(object sender, EventArgs e)
        {
            // Clear any existing results.
            _myMapView.Map.OperationalLayers.Clear();

            // Show the animating progress bar .
            _progressBar.StartAnimating();

            // Get the 'from' and 'to' dates from the date pickers for the geoprocessing analysis.
            DateTime fromDate = (DateTime) _selectionView.StartPicker.Date;
            DateTime toDate = (DateTime) _selectionView.EndPicker.Date;

            // The end date must be at least one day after the start date.
            if (toDate <= fromDate.AddDays(1))
            {
                // Show error message.
                UIAlertController alert = UIAlertController.Create("Invalid date range",
                    "Please enter a valid date range. There has to be at least one day in between To and From dates.", UIAlertControllerStyle.Alert);
                alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                PresentViewController(alert, true, null);

                // Stop the progress bar from animating (which also hides it as well).
                _progressBar.StopAnimating();

                return;
            }

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

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

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

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

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

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

                // Zoom to the results.
                await _myMapView.SetViewpointAsync(new Viewpoint(analysisResult.MapImageLayer.FullExtent));
            }
            catch (TaskCanceledException)
            {
                // This is thrown if the task is canceled. Ignore.
            }
            catch (Exception ex)
            {
                // Display error messages if the geoprocessing task fails.
                if (_hotspotJob.Status == JobStatus.Failed && _hotspotJob.Error != null)
                {
                    // Report error.
                    UIAlertController alert = UIAlertController.Create("Geoprocessing Error", _hotspotJob.Error.Message, UIAlertControllerStyle.Alert);
                    alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                    PresentViewController(alert, true, null);
                }
                else
                {
                    // Report error.
                    UIAlertController alert = UIAlertController.Create("Sample error", ex.ToString(), UIAlertControllerStyle.Alert);
                    alert.AddAction(UIAlertAction.Create("OK", UIAlertActionStyle.Default, null));
                    PresentViewController(alert, true, null);
                }
            }
            finally
            {
                // Stop the progress bar from animating (which also hides it).
                _progressBar.StopAnimating();
            }
        }

        private void ShowConfiguration(object sender, EventArgs e)
        {
            NavigationController.PushViewController(_selectionView, true);
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            Initialize();
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView {BackgroundColor = ApplicationTheme.BackgroundColor};

            _selectionView = new DateSelectionViewController();

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _configureButton = new UIBarButtonItem();
            _configureButton.Title = "Configure";

            _startButton = new UIBarButtonItem();
            _startButton.Title = "Run analysis";

            UIToolbar toolbar = new UIToolbar();
            toolbar.TranslatesAutoresizingMaskIntoConstraints = false;
            toolbar.Items = new[]
            {
                _configureButton,
                new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace),
                _startButton
            };

            // Hide the activity indicator (progress bar) when stopped.
            _progressBar = new UIActivityIndicatorView(UIActivityIndicatorViewStyle.WhiteLarge)
            {
                BackgroundColor = UIColor.FromWhiteAlpha(0, .5f),
                HidesWhenStopped = true,
                TranslatesAutoresizingMaskIntoConstraints = false
            };

            // Add the views.
            View.AddSubviews(_myMapView, toolbar, _progressBar);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
            {
                _myMapView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(toolbar.TopAnchor),
                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                toolbar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                toolbar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                toolbar.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),

                _progressBar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _progressBar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                _progressBar.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _progressBar.BottomAnchor.ConstraintEqualTo(View.BottomAnchor)
            });
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _startButton.Clicked += OnRunAnalysisClicked;
            _configureButton.Clicked += ShowConfiguration;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _startButton.Clicked -= OnRunAnalysisClicked;
            _configureButton.Clicked -= ShowConfiguration;
        }
    }
}

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