Perform a feature analysis

Run a find hot spot analysis on traffic and parking violations in San Francisco.

A feature analysis is the process of using the spatial analysis service to perform server-side geometric and analytic operations on feature data. All feature analysis requests are job requests. The easiest way to programmatically run an analysis request to the spatial analysis service is to use ArcGIS REST JS, which provides a Job class that handles long- running operations.

In this tutorial, you use ArcGIS REST JS to perform a hot spot analysis to find statistically significant clusters of parking violations.

Prerequisites

You need the following to access the spatial analysis service and perform feature analysis operations:

An ArcGIS Online account.
A registered application to obtain its Client ID.
The redirect URL of the registered application to use for authentication in the format "https://<server>[:port]" as in: https://localhost:8080.

Steps

Download the starter code

Download the tutorial starter code zip file from ArcGIS Online.

The zip file contains the following:

feature-analysis.html
authenticate.html

The feature-analysis.html file contains basic HTML scaffolding and the OAuth 2.0 code necessary to perform the analysis. The authenticate.html file is the callback page used as part of the authentication process.

Configure authentication

To access the spatial analysis service, you need an ArcGIS Online account and provide authentication using ArcGIS identity, which creates a temporary token using OAuth 2.0 protocol. API keys are not supported.

Use the ArcGISIdentityManager class from ArcGIS REST JS to configure ArcGIS identity authentication.

Go to the developer dashboard > OAuth2.0 tab and copy your application's Client ID.

In the authenticate.html file, replace YOUR_CLIENT_ID with your Client ID.

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    <script type="module">
      import { ArcGISIdentityManager } from 'https://cdn.skypack.dev/@esri/arcgis-rest-request@4.0.0';

      const clientId = "YOUR_CLIENT_ID";

      const redirectUri = "authenticate.html";
      ArcGISIdentityManager.completeOAuth2({
        clientId,
        redirectUri
      })
    </script>
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In the feature-analysis.html file, replace YOUR_CLIENT_ID with your Client ID.

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      const clientId = 'YOUR_CLIENT_ID';

      const signInLabel = "Sign in";

      const acctErrorMsg =
        "You can only access the spatial analysis service if you have an ArcGIS Online account and you use <a href='https://developers.arcgis.com/documentation/mapping-apis-and-services/security/arcgis-identity/'>ArcGIS identity</a> to authenticate requests to the service. ArcGIS Developer accounts and API keys are not supported. However, if you have an ArcGIS Developer account and would like to access the service, please contact <a href='https://www.esri.com/en-us/contact'>Esri.</a>";
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Run the application and navigate to your localhost, for example https://localhost:8080.

You should be able to click the Sign in button and successfully log in to an ArcGIS Online account.

Display parking violations

To perform feature analysis, you need to provide feature data as input. In this tutorial, you use the SF parking violations hosted feature layer as input data for the hot spot analysis.

Add the parking violation feature layer and the corresponding vector tile layer to the points and pointsVTL variables.

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      const acctErrorMsg =
        "You can only access the spatial analysis service if you have an ArcGIS Online account and you use <a href='https://developers.arcgis.com/documentation/mapping-apis-and-services/security/arcgis-identity/'>ArcGIS identity</a> to authenticate requests to the service. ArcGIS Developer accounts and API keys are not supported. However, if you have an ArcGIS Developer account and would like to access the service, please contact <a href='https://www.esri.com/en-us/contact'>Esri.</a>";

      const points =
        'https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/sf_traffic_parking_violations_sa_osapi/FeatureServer/0';

      const pointsVTL =
        'https://vectortileservices3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/sf_traffic_parking_violations_sa_osapi/VectorTileServer';

      // This layer contains the results of a hot spot analysis executes on the points layer. You can use it to verify that your program is working.
      const sampleResults =
        'https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/sf_osapi_driveways_sidewalk_hot_spots/FeatureServer/0';

      // You may need to modify this path to reflect your actual file structure
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Create a map and set the session.token to display a basemap layer.

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      const initMap = (withToken) => {
        // create map and add basemap
        const baseMapEnum = 'ArcGIS:HumanGeography';

        map = new maplibregl.Map({
          container: 'map',
          style: `https://basemaps-api.arcgis.com/arcgis/rest/services/styles/${baseMapEnum}?type=style&token=${withToken}`,
          center: [-122.44571685791017, 37.76053707395286],
          zoom: 11,
        });


      };

      const updateSessionInfo = (session) => {
        let sessionInfo = document.getElementById('withPopupButton');

        if (session) {
          sessionInfo.innerHTML = `Sign out : ${session.username}`;
          localStorage.setItem(
            '__ARCGIS_REST_USER_SESSION__',
            session.serialize()
          );

          initMap(session.token);

          document.getElementById('signInModal').open = false;
          document.getElementById('runAnalysisBtn').disabled = false;
        } else {
          sessionInfo.innerHTML = signInLabel;
          if (map) {
            map.off();
            map.remove();
          }
          document.getElementById('signInModal').open = true;
          document.getElementById('runAnalysisBtn').disabled = true;
        }
      };
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Create a style definition for the parking violatons layer.

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      let session = null;
      let map = null;

      let vtlLayer = {
        id: 'vtlLayer',
        type: 'circle',
        source: 'violations',
        'source-layer': 'DeriveNewLocationsOutput',
        paint: {
          'circle-color': 'rgb(0,0,0)',
          'circle-radius': 1.5,
        },
      };
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Add the SF parking violations vector tile layer to the map.

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      const initMap = (withToken) => {
        // create map and add basemap
        const baseMapEnum = 'ArcGIS:HumanGeography';

        map = new maplibregl.Map({
          container: 'map',
          style: `https://basemaps-api.arcgis.com/arcgis/rest/services/styles/${baseMapEnum}?type=style&token=${withToken}`,
          center: [-122.44571685791017, 37.76053707395286],
          zoom: 11,
        });


        let lastResultUrl = null;

        map.once('load', () => {
          map.addSource('violations', {
            type: 'vector',
            tiles: [`${pointsVTL}/tile/{z}/{y}/{x}.pbf`],
          });

          map.addLayer(vtlLayer);

      };
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Run the application and navigate to your localhost, for example https://localhost:8080. After you sign in, you will see the vector tile layer rendered on the map.

Get the analysis URL

To make a request to the spatial analysis service, you need to get the URL first. The analysis service URL is unique to your organization.

Call the getSelf operation from ArcGIS REST JS to obtain the analysis URL.

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      const getAnalysisUrl = async (withAuth) => {
        const portalSelf = await getSelf({
          authentication: withAuth,
        });

        return portalSelf.helperServices.analysis.url;
      };


      document
        .getElementById('withPopupButton')
        .addEventListener('click', getAuth);
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Make the request

Use the Job class and set the operationURL and params required for the selected analysis.

Create a function that submits a Job request to the spatial analysis service using your organization's analysis URL. Set the params required for a hot spot analysis and authenticate using the session token.

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      const getAnalysisUrl = async (withAuth) => {
        const portalSelf = await getSelf({
          authentication: withAuth,
        });

        return portalSelf.helperServices.analysis.url;
      };

      const runAnalysis = async () => {
        const analysisUrl = await getAnalysisUrl(session);
        const operationUrl = `${analysisUrl}/FindHotSpots/submitJob`;
        const params = {
          analysisLayer: { url: points },
          shapeType: 'Hexagon',
          outputName: {
            serviceProperties: {
              name: `MapLibreGLJS_find_hot_spots_${new Date().getTime()}`,
            },
          }, //Outputs results as a hosted feature serivce.
        };

        const jobReq = await Job.submitJob({
          url: operationUrl,
          params: params,
          authentication: session,
        });

        // listen to the status event to get updates every time the job status is checked.
        jobReq.on(JOB_STATUSES.Status, (jobInfo) => {
          console.log(jobInfo.status);
        });

        // get all the results, this will start monitoring and trigger events
        const jobResp = await jobReq.getAllResults();

        // jobResp.aggregatedLayer.value.url
        return jobResp;
      };
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Call the runAnalysis function to run the operation.

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      const runAnalysisBtnWasClicked = (evt) => {
        document.getElementById('runAnalysisBtn').hidden = true;
        document.getElementById('progressBar').hidden = false;
        document.getElementById('withPopupButton').disabled = true;

        runAnalysis().then(
          (results) => {
            document.getElementById('runAnalysisBtn').hidden = false;
            document.getElementById('progressBar').hidden = true;
            document.getElementById('withPopupButton').disabled = false;

          },
          (err) => {
            console.log(err);
            document.getElementById('progressBar').hidden = true;
            document.getElementById('runAnalysisBtn').hidden = false;
            document.getElementById('withPopupButton').disabled = false;
            showAlert(err);
          }
        );

      };
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Display results

The results of a feature analysis are returned as feature data.

Create a style definition for the analysis result layer.

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