Point clustering - query clusters

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This sample demonstrates how to query features represented by aggregate point clusters. Clustering is a method of reducing points in a FeatureLayer, CSVLayer, GeoJSONLayer, or OGCFeatureLayer by grouping them into clusters based on their spatial proximity to one another. Typically, clusters are proportionally sized based on the number of features within each cluster. See the Point clustering - basic configuration if you are unfamiliar with clustering.

Querying clustered features allows you to do the following:

  1. Query and display statistics describing the clustered features in the popup.
  2. Query the extent of the features and display it in the view.
  3. Query all features and calculate the convex hull.

To query a cluster's features, you must provide the ObjectID of the graphic representing the cluster to the Query.aggregateIds property and pass the parameters to the desired query method on the clustered layer's layer view.

Query cluster features
                                                                                                                                                                                                                                                                                                                                                                      
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta
  name="viewport"
  content="initial-scale=1,maximum-scale=1,user-scalable=no"
/>

<title>Point clustering - query clusters | Sample | ArcGIS API for JavaScript 4.19</title>

<link rel="stylesheet" href="https://js.arcgis.com/4.19/esri/themes/light/main.css" />
<script src="https://js.arcgis.com/4.19/"></script>

<style>
  html,
  body,
  #viewDiv {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
    background-color: white;
  }
  #infoDiv {
    background: white;
    padding: 10px;
  }
  table td {
    padding: 3px;
  }

  table.popup td.num {
    text-align: right;
  }

  table.popup tr.head {
    text-align: center;
    font-weight: bold;
    background-color:rgba(50, 50, 50,0.08);
  }

  .table-container {
    width:100%;
    height:100%;
    text-align: center;
  }

  table {
    margin: 0 auto;
  }
</style>

<script>
  require([
    "esri/WebMap",
    "esri/Graphic",
    "esri/views/MapView",
    "esri/layers/FeatureLayer",
    "esri/widgets/Legend",
    "esri/widgets/Expand",
    "esri/smartMapping/labels/clusters",
    "esri/smartMapping/popup/clusters",
    "esri/core/watchUtils",
    "esri/symbols/support/symbolUtils",
    "esri/geometry/geometryEngine",
  ], (
    WebMap,
    Graphic,
    MapView,
    FeatureLayer,
    Legend,
    Expand,
    clusterLabelCreator,
    clusterPopupCreator,
    watchUtils,
    symbolUtils,
    geometryEngine
  ) => {

    let layerView;

    const layer = new FeatureLayer({
      portalItem: {
        id: "eb54b44c65b846cca12914b87b315169"
      },
      outFields: [ "capacity_mw" ]
    });

    const map = new WebMap({
      basemap: {
        portalItem: {
          id: "75a08e8cd8b64dcfa6945bb7f624ccc5"
        }
      },
      layers: [ layer ]
    });

    const view = new MapView({
      container: "viewDiv",
      map,
      extent: {
        spatialReference: {
          latestWkid: 3857,
          wkid: 102100
        },
        xmin: -15327459,
        ymin: 2740044,
        xmax: -6076744,
        ymax: 6878650
      },
      popup: {
        dockEnabled: true,
        dockOptions: {
          breakpoint: false,
          position: "top-right"
        }
      }
    });

    view.ui.add( new Expand({
      content: new Legend({ view }),
      view
    }), "top-left");

    layer
      .when()
      .then(generateClusterConfig)
      .then( async (featureReduction) => {

        // sets generated cluster configuration on the layer
        layer.featureReduction = featureReduction;

        // the layer view is needed for querying clusters
        layerView = await view.whenLayerView(layer);

        // Disable clustering when user zooms beyond a 1:50,000 scale level
        // Re-enable clustering when the user zooms out to a scale smaller than 1:50,000
        view.watch("scale", (scale) => {
          layer.featureReduction = view.scale > 50000 ? featureReduction : null;
        });
      })
      .catch((error) => {
        console.error(error);
      });

    async function generateClusterConfig(layer) {
      // generates default popupTemplate
      const popupTemplate =
        await clusterPopupCreator
          .getTemplates({
            layer
          })
          .then((popupTemplateResponse) => popupTemplateResponse.primaryTemplate.value);

      // Add actions for exploring the features of each cluster
      popupTemplate.actions = [
        {
          title: "Statistics",
          id: "statistics",
          className: "esri-icon-line-chart"
        },
        {
          title: "Convex hull",
          id: "convex-hull",
          className: "esri-icon-polygon"
        },
        {
          title: "Show features",
          id: "show-features",
          className: "esri-icon-maps"
        }
      ];

      // generates default labelingInfo
      const { labelingInfo, clusterMinSize } =
        await clusterLabelCreator
          .getLabelSchemes({
            layer, view
          })
          .then((labelSchemes) => labelSchemes.primaryScheme);

      return {
        type: "cluster",
        popupTemplate,
        labelingInfo,
        clusterMinSize
      };
    }

    view.popup.on("trigger-action", (event) => {
      clearViewGraphics();

      const popup = view.popup;
      const selectedFeature = popup.selectedFeature && popup.selectedFeature.isAggregate

      const id = event.action.id;

      if(id === "convex-hull"){
        displayConvexHull(view.popup.selectedFeature);
      }
      if(id === "show-features"){
        displayFeatures(view.popup.selectedFeature);
      }
      if(id === "statistics"){
        calculateStatistics(view.popup.selectedFeature);
      }
    });

    watchUtils.watch(view, ["scale", "popup.selectedFeature", "popup.visible"], clearViewGraphics);

    let convexHullGraphic = null;
    let clusterChildGraphics = [];

    function clearViewGraphics(){
      view.graphics.remove(convexHullGraphic);
      view.graphics.removeMany(clusterChildGraphics);
    }

    // displays all features from a given cluster in the view
    async function displayFeatures(graphic){
      processParams(graphic, layerView);


      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);


      features.forEach( async (feature) => {
        const symbol = await symbolUtils.getDisplayedSymbol(feature)
        feature.symbol = symbol;
        view.graphics.add(feature);
      });
      clusterChildGraphics = features;
    }


    async function displayConvexHull(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);
      const geometries = features.map( feature => feature.geometry );
      const [ convexHull ] = geometryEngine.convexHull(geometries, true);

      convexHullGraphic = new Graphic({
        geometry: convexHull,
        symbol: {
          type: "simple-fill",
          outline: {
            width: 1.5,
            color: [ 75, 75, 75, 1 ]
          },
          style: "none",
          color: [ 0, 0, 0, 0.1 ]
        }
      });
      view.graphics.add(convexHullGraphic);
    }


    // calculates set statistics for features in a cluster
    // and displays them in the cluster popup

    async function calculateStatistics(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();

      query.aggregateIds = [graphic.getObjectId()];

      query.groupByFieldsForStatistics = [ "fuel1" ];
      query.outFields = [ "capacity_mw", "fuel1" ];
      query.orderByFields = [ "num_features desc" ];
      query.outStatistics = [
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_total",
          statisticType: "sum"
        },
        {
          onStatisticField: "1",
          outStatisticFieldName: "num_features",
          statisticType: "count"
        },
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_max",
          statisticType: "max"
        }
      ];

      const { features } = await layerView.queryFeatures(query);
      const stats = features.map( feature => feature.attributes);


      let table = `
        <div class="table-container">
          <span style="font-size: 14pt"><strong>Summary by fuel type</strong></span>
          <br/>
          <br/>
          <table class="esri-widget popup">
            <tr class="head"><td>Fuel</td><td>Count</td><td>Capacity (mW)</td><td>Largest plant (mW)</td></tr>
      `;

      let totalCapacity = 0;
      let totalCount = 0;

      stats.forEach( stat => {
        const fuel = stat.fuel1;
        const total = stat.capacity_total;
        const max = stat.capacity_max;
        const count = stat.num_features;

        totalCapacity += total;
        totalCount += count;

        table += `
          <tr><td><span style:'font-weight:bolder'>${fuel}</span></td><td class="num">${count}</td><td class="num">${roundDecimals(total, 2).toLocaleString()}</td><td class="num">${roundDecimals(max, 2).toLocaleString()}</td></tr>
        `;
      });

      table += `
        </table>
      </div>`;

      view.popup.content = `
        <div style="font-size: 12pt">
        Number of features: <strong>${totalCount.toLocaleString()}</strong><br>
        Total capacity (mW): <strong>${roundDecimals(totalCapacity, 2).toLocaleString()}</strong><br>
        </div><br>
      ` + table;
    }


    function processParams(graphic, layerView){
      if (!graphic || !layerView) {
        throw new Error("Graphic or layerView not provided.");
      }

      if (!graphic.isAggregate) {
        throw new Error("Graphic must represent a cluster.");
      }
    }

    function roundDecimals(num, places){
      return Math.round(num * Math.pow(10, places)) / Math.pow(10, places);
    }
  });
</script>
</head>

<body>
<div id="viewDiv"></div>
</body>
</html>

Query cluster statistics

To query statistics for the features included in a cluster, reference the ObjectID of the cluster graphic in Query.aggregateIds, then specify the query outStatistics. Since the clustered layer has a UniqueValueRenderer, we'll use groupByFieldsForStatistics to group the statistics by the field used to categorize the features in the renderer.

cluster statistics

Calculate cluster statistics
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta
  name="viewport"
  content="initial-scale=1,maximum-scale=1,user-scalable=no"
/>

<title>Point clustering - query clusters | Sample | ArcGIS API for JavaScript 4.19</title>

<link rel="stylesheet" href="https://js.arcgis.com/4.19/esri/themes/light/main.css" />
<script src="https://js.arcgis.com/4.19/"></script>

<style>
  html,
  body,
  #viewDiv {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
    background-color: white;
  }
  #infoDiv {
    background: white;
    padding: 10px;
  }
  table td {
    padding: 3px;
  }

  table.popup td.num {
    text-align: right;
  }

  table.popup tr.head {
    text-align: center;
    font-weight: bold;
    background-color:rgba(50, 50, 50,0.08);
  }

  .table-container {
    width:100%;
    height:100%;
    text-align: center;
  }

  table {
    margin: 0 auto;
  }
</style>

<script>
  require([
    "esri/WebMap",
    "esri/Graphic",
    "esri/views/MapView",
    "esri/layers/FeatureLayer",
    "esri/widgets/Legend",
    "esri/widgets/Expand",
    "esri/smartMapping/labels/clusters",
    "esri/smartMapping/popup/clusters",
    "esri/core/watchUtils",
    "esri/symbols/support/symbolUtils",
    "esri/geometry/geometryEngine",
  ], (
    WebMap,
    Graphic,
    MapView,
    FeatureLayer,
    Legend,
    Expand,
    clusterLabelCreator,
    clusterPopupCreator,
    watchUtils,
    symbolUtils,
    geometryEngine
  ) => {

    let layerView;

    const layer = new FeatureLayer({
      portalItem: {
        id: "eb54b44c65b846cca12914b87b315169"
      },
      outFields: [ "capacity_mw" ]
    });

    const map = new WebMap({
      basemap: {
        portalItem: {
          id: "75a08e8cd8b64dcfa6945bb7f624ccc5"
        }
      },
      layers: [ layer ]
    });

    const view = new MapView({
      container: "viewDiv",
      map,
      extent: {
        spatialReference: {
          latestWkid: 3857,
          wkid: 102100
        },
        xmin: -15327459,
        ymin: 2740044,
        xmax: -6076744,
        ymax: 6878650
      },
      popup: {
        dockEnabled: true,
        dockOptions: {
          breakpoint: false,
          position: "top-right"
        }
      }
    });

    view.ui.add( new Expand({
      content: new Legend({ view }),
      view
    }), "top-left");

    layer
      .when()
      .then(generateClusterConfig)
      .then( async (featureReduction) => {

        // sets generated cluster configuration on the layer
        layer.featureReduction = featureReduction;

        // the layer view is needed for querying clusters
        layerView = await view.whenLayerView(layer);

        // Disable clustering when user zooms beyond a 1:50,000 scale level
        // Re-enable clustering when the user zooms out to a scale smaller than 1:50,000
        view.watch("scale", (scale) => {
          layer.featureReduction = view.scale > 50000 ? featureReduction : null;
        });
      })
      .catch((error) => {
        console.error(error);
      });

    async function generateClusterConfig(layer) {
      // generates default popupTemplate
      const popupTemplate =
        await clusterPopupCreator
          .getTemplates({
            layer
          })
          .then((popupTemplateResponse) => popupTemplateResponse.primaryTemplate.value);

      // Add actions for exploring the features of each cluster
      popupTemplate.actions = [
        {
          title: "Statistics",
          id: "statistics",
          className: "esri-icon-line-chart"
        },
        {
          title: "Convex hull",
          id: "convex-hull",
          className: "esri-icon-polygon"
        },
        {
          title: "Show features",
          id: "show-features",
          className: "esri-icon-maps"
        }
      ];

      // generates default labelingInfo
      const { labelingInfo, clusterMinSize } =
        await clusterLabelCreator
          .getLabelSchemes({
            layer, view
          })
          .then((labelSchemes) => labelSchemes.primaryScheme);

      return {
        type: "cluster",
        popupTemplate,
        labelingInfo,
        clusterMinSize
      };
    }

    view.popup.on("trigger-action", (event) => {
      clearViewGraphics();

      const popup = view.popup;
      const selectedFeature = popup.selectedFeature && popup.selectedFeature.isAggregate

      const id = event.action.id;

      if(id === "convex-hull"){
        displayConvexHull(view.popup.selectedFeature);
      }
      if(id === "show-features"){
        displayFeatures(view.popup.selectedFeature);
      }
      if(id === "statistics"){
        calculateStatistics(view.popup.selectedFeature);
      }
    });

    watchUtils.watch(view, ["scale", "popup.selectedFeature", "popup.visible"], clearViewGraphics);

    let convexHullGraphic = null;
    let clusterChildGraphics = [];

    function clearViewGraphics(){
      view.graphics.remove(convexHullGraphic);
      view.graphics.removeMany(clusterChildGraphics);
    }

    // displays all features from a given cluster in the view
    async function displayFeatures(graphic){
      processParams(graphic, layerView);


      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);


      features.forEach( async (feature) => {
        const symbol = await symbolUtils.getDisplayedSymbol(feature)
        feature.symbol = symbol;
        view.graphics.add(feature);
      });
      clusterChildGraphics = features;
    }


    async function displayConvexHull(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);
      const geometries = features.map( feature => feature.geometry );
      const [ convexHull ] = geometryEngine.convexHull(geometries, true);

      convexHullGraphic = new Graphic({
        geometry: convexHull,
        symbol: {
          type: "simple-fill",
          outline: {
            width: 1.5,
            color: [ 75, 75, 75, 1 ]
          },
          style: "none",
          color: [ 0, 0, 0, 0.1 ]
        }
      });
      view.graphics.add(convexHullGraphic);
    }


    // calculates set statistics for features in a cluster
    // and displays them in the cluster popup

    async function calculateStatistics(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();

      query.aggregateIds = [graphic.getObjectId()];

      query.groupByFieldsForStatistics = [ "fuel1" ];
      query.outFields = [ "capacity_mw", "fuel1" ];
      query.orderByFields = [ "num_features desc" ];
      query.outStatistics = [
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_total",
          statisticType: "sum"
        },
        {
          onStatisticField: "1",
          outStatisticFieldName: "num_features",
          statisticType: "count"
        },
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_max",
          statisticType: "max"
        }
      ];

      const { features } = await layerView.queryFeatures(query);
      const stats = features.map( feature => feature.attributes);


      let table = `
        <div class="table-container">
          <span style="font-size: 14pt"><strong>Summary by fuel type</strong></span>
          <br/>
          <br/>
          <table class="esri-widget popup">
            <tr class="head"><td>Fuel</td><td>Count</td><td>Capacity (mW)</td><td>Largest plant (mW)</td></tr>
      `;

      let totalCapacity = 0;
      let totalCount = 0;

      stats.forEach( stat => {
        const fuel = stat.fuel1;
        const total = stat.capacity_total;
        const max = stat.capacity_max;
        const count = stat.num_features;

        totalCapacity += total;
        totalCount += count;

        table += `
          <tr><td><span style:'font-weight:bolder'>${fuel}</span></td><td class="num">${count}</td><td class="num">${roundDecimals(total, 2).toLocaleString()}</td><td class="num">${roundDecimals(max, 2).toLocaleString()}</td></tr>
        `;
      });

      table += `
        </table>
      </div>`;

      view.popup.content = `
        <div style="font-size: 12pt">
        Number of features: <strong>${totalCount.toLocaleString()}</strong><br>
        Total capacity (mW): <strong>${roundDecimals(totalCapacity, 2).toLocaleString()}</strong><br>
        </div><br>
      ` + table;
    }


    function processParams(graphic, layerView){
      if (!graphic || !layerView) {
        throw new Error("Graphic or layerView not provided.");
      }

      if (!graphic.isAggregate) {
        throw new Error("Graphic must represent a cluster.");
      }
    }

    function roundDecimals(num, places){
      return Math.round(num * Math.pow(10, places)) / Math.pow(10, places);
    }
  });
</script>
</head>

<body>
<div id="viewDiv"></div>
</body>
</html>

Query cluster extent

You may want to display the extent of clustered features to the user. To do this, reference the cluster graphic's ObjectID in Query.aggregateIds, and call the queryExtent method on the layer view.

cluster query extent

                   
async function displayClusterExtent(graphic){
  const query = layerView.createQuery();
  query.aggregateIds = [ graphic.getObjectId() ];

  const { extent } = await layerView.queryExtent(query);
  const extentGraphic = {
    geometry: extent,
    symbol: {
      type: "simple-fill",
      outline: {
        width: 1.5,
        color: [ 75, 75, 75, 1 ]
      },
      style: "none",
      color: [ 0, 0, 0, 0.1 ]
    }
  };
  view.graphics.add(extentGraphic);
}

The cluster popup already displays the cluster extent by default when the browse features action is clicked.

Display cluster convex hull

Perhaps it's better to show the convex hull of the clustered features rather than the extent since it more accurately represents the distribution of the points. The geometryEngine allows you to do that. Query for all the features in the cluster, get their geometries, then pass them to the convexHull method of geometryEngine.

cluster convex hull

Display cluster convex hull
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta
  name="viewport"
  content="initial-scale=1,maximum-scale=1,user-scalable=no"
/>

<title>Point clustering - query clusters | Sample | ArcGIS API for JavaScript 4.19</title>

<link rel="stylesheet" href="https://js.arcgis.com/4.19/esri/themes/light/main.css" />
<script src="https://js.arcgis.com/4.19/"></script>

<style>
  html,
  body,
  #viewDiv {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
    background-color: white;
  }
  #infoDiv {
    background: white;
    padding: 10px;
  }
  table td {
    padding: 3px;
  }

  table.popup td.num {
    text-align: right;
  }

  table.popup tr.head {
    text-align: center;
    font-weight: bold;
    background-color:rgba(50, 50, 50,0.08);
  }

  .table-container {
    width:100%;
    height:100%;
    text-align: center;
  }

  table {
    margin: 0 auto;
  }
</style>

<script>
  require([
    "esri/WebMap",
    "esri/Graphic",
    "esri/views/MapView",
    "esri/layers/FeatureLayer",
    "esri/widgets/Legend",
    "esri/widgets/Expand",
    "esri/smartMapping/labels/clusters",
    "esri/smartMapping/popup/clusters",
    "esri/core/watchUtils",
    "esri/symbols/support/symbolUtils",
    "esri/geometry/geometryEngine",
  ], (
    WebMap,
    Graphic,
    MapView,
    FeatureLayer,
    Legend,
    Expand,
    clusterLabelCreator,
    clusterPopupCreator,
    watchUtils,
    symbolUtils,
    geometryEngine
  ) => {

    let layerView;

    const layer = new FeatureLayer({
      portalItem: {
        id: "eb54b44c65b846cca12914b87b315169"
      },
      outFields: [ "capacity_mw" ]
    });

    const map = new WebMap({
      basemap: {
        portalItem: {
          id: "75a08e8cd8b64dcfa6945bb7f624ccc5"
        }
      },
      layers: [ layer ]
    });

    const view = new MapView({
      container: "viewDiv",
      map,
      extent: {
        spatialReference: {
          latestWkid: 3857,
          wkid: 102100
        },
        xmin: -15327459,
        ymin: 2740044,
        xmax: -6076744,
        ymax: 6878650
      },
      popup: {
        dockEnabled: true,
        dockOptions: {
          breakpoint: false,
          position: "top-right"
        }
      }
    });

    view.ui.add( new Expand({
      content: new Legend({ view }),
      view
    }), "top-left");

    layer
      .when()
      .then(generateClusterConfig)
      .then( async (featureReduction) => {

        // sets generated cluster configuration on the layer
        layer.featureReduction = featureReduction;

        // the layer view is needed for querying clusters
        layerView = await view.whenLayerView(layer);

        // Disable clustering when user zooms beyond a 1:50,000 scale level
        // Re-enable clustering when the user zooms out to a scale smaller than 1:50,000
        view.watch("scale", (scale) => {
          layer.featureReduction = view.scale > 50000 ? featureReduction : null;
        });
      })
      .catch((error) => {
        console.error(error);
      });

    async function generateClusterConfig(layer) {
      // generates default popupTemplate
      const popupTemplate =
        await clusterPopupCreator
          .getTemplates({
            layer
          })
          .then((popupTemplateResponse) => popupTemplateResponse.primaryTemplate.value);

      // Add actions for exploring the features of each cluster
      popupTemplate.actions = [
        {
          title: "Statistics",
          id: "statistics",
          className: "esri-icon-line-chart"
        },
        {
          title: "Convex hull",
          id: "convex-hull",
          className: "esri-icon-polygon"
        },
        {
          title: "Show features",
          id: "show-features",
          className: "esri-icon-maps"
        }
      ];

      // generates default labelingInfo
      const { labelingInfo, clusterMinSize } =
        await clusterLabelCreator
          .getLabelSchemes({
            layer, view
          })
          .then((labelSchemes) => labelSchemes.primaryScheme);

      return {
        type: "cluster",
        popupTemplate,
        labelingInfo,
        clusterMinSize
      };
    }

    view.popup.on("trigger-action", (event) => {
      clearViewGraphics();

      const popup = view.popup;
      const selectedFeature = popup.selectedFeature && popup.selectedFeature.isAggregate

      const id = event.action.id;

      if(id === "convex-hull"){
        displayConvexHull(view.popup.selectedFeature);
      }
      if(id === "show-features"){
        displayFeatures(view.popup.selectedFeature);
      }
      if(id === "statistics"){
        calculateStatistics(view.popup.selectedFeature);
      }
    });

    watchUtils.watch(view, ["scale", "popup.selectedFeature", "popup.visible"], clearViewGraphics);

    let convexHullGraphic = null;
    let clusterChildGraphics = [];

    function clearViewGraphics(){
      view.graphics.remove(convexHullGraphic);
      view.graphics.removeMany(clusterChildGraphics);
    }

    // displays all features from a given cluster in the view
    async function displayFeatures(graphic){
      processParams(graphic, layerView);


      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);


      features.forEach( async (feature) => {
        const symbol = await symbolUtils.getDisplayedSymbol(feature)
        feature.symbol = symbol;
        view.graphics.add(feature);
      });
      clusterChildGraphics = features;
    }


    async function displayConvexHull(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();
      query.aggregateIds = [graphic.getObjectId()];
      const { features } = await layerView.queryFeatures(query);
      const geometries = features.map( feature => feature.geometry );
      const [ convexHull ] = geometryEngine.convexHull(geometries, true);

      convexHullGraphic = new Graphic({
        geometry: convexHull,
        symbol: {
          type: "simple-fill",
          outline: {
            width: 1.5,
            color: [ 75, 75, 75, 1 ]
          },
          style: "none",
          color: [ 0, 0, 0, 0.1 ]
        }
      });
      view.graphics.add(convexHullGraphic);
    }


    // calculates set statistics for features in a cluster
    // and displays them in the cluster popup

    async function calculateStatistics(graphic){
      processParams(graphic, layerView);

      const query = layerView.createQuery();

      query.aggregateIds = [graphic.getObjectId()];

      query.groupByFieldsForStatistics = [ "fuel1" ];
      query.outFields = [ "capacity_mw", "fuel1" ];
      query.orderByFields = [ "num_features desc" ];
      query.outStatistics = [
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_total",
          statisticType: "sum"
        },
        {
          onStatisticField: "1",
          outStatisticFieldName: "num_features",
          statisticType: "count"
        },
        {
          onStatisticField: "capacity_mw",
          outStatisticFieldName: "capacity_max",
          statisticType: "max"
        }
      ];

      const { features } = await layerView.queryFeatures(query);
      const stats = features.map( feature => feature.attributes);


      let table = `
        <div class="table-container">
          <span style="font-size: 14pt"><strong>Summary by fuel type</strong></span>
          <br/>
          <br/>
          <table class="esri-widget popup">
            <tr class="head"><td>Fuel</td><td>Count</td><td>Capacity (mW)</td><td>Largest plant (mW)</td></tr>
      `;

      let totalCapacity = 0;
      let totalCount = 0;

      stats.forEach( stat => {
        const fuel = stat.fuel1;
        const total = stat.capacity_total;
        const max = stat.capacity_max;
        const count = stat.num_features;

        totalCapacity += total;
        totalCount += count;

        table += `
          <tr><td><span style:'font-weight:bolder'>${fuel}</span></td><td class="num">${count}</td><td class="num">${roundDecimals(total, 2).toLocaleString()}</td><td class="num">${roundDecimals(max, 2).toLocaleString()}</td></tr>
        `;
      });

      table += `
        </table>
      </div>`;

      view.popup.content = `
        <div style="font-size: 12pt">
        Number of features: <strong>${totalCount.toLocaleString()}</strong><br>
        Total capacity (mW): <strong>${roundDecimals(totalCapacity, 2).toLocaleString()}</strong><br>
        </div><br>
      ` + table;
    }


    function processParams(graphic, layerView){
      if (!graphic || !layerView) {
        throw new Error("Graphic or layerView not provided.");
      }

      if (!graphic.isAggregate) {
        throw new Error("Graphic must represent a cluster.");
      }
    }

    function roundDecimals(num, places){
      return Math.round(num * Math.pow(10, places)) / Math.pow(10, places);
    }
  });
</script>
</head>

<body>
<div id="viewDiv"></div>
</body>
</html>