Styling clusters

Customizing the display of clusters and markers with L.DivIcon and L.MarkerClusterGroup options. More information about Feature Layers can be found in the L.esri.FeatureLayer documentation.
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Styling clusters</title>
  <meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" />

  <!-- Load Leaflet from CDN -->
  <link rel="stylesheet" href="https://unpkg.com/leaflet@1.7.1/dist/leaflet.css"
    integrity="sha512-xodZBNTC5n17Xt2atTPuE1HxjVMSvLVW9ocqUKLsCC5CXdbqCmblAshOMAS6/keqq/sMZMZ19scR4PsZChSR7A=="
    crossorigin=""/>
  <script src="https://unpkg.com/leaflet@1.7.1/dist/leaflet.js"
    integrity="sha512-XQoYMqMTK8LvdxXYG3nZ448hOEQiglfqkJs1NOQV44cWnUrBc8PkAOcXy20w0vlaXaVUearIOBhiXZ5V3ynxwA=="
    crossorigin=""></script>

  <!-- Load Esri Leaflet from CDN -->
  <script src="https://unpkg.com/esri-leaflet@3.0.8/dist/esri-leaflet.js"
    integrity="sha512-E0DKVahIg0p1UHR2Kf9NX7x7TUewJb30mxkxEm2qOYTVJObgsAGpEol9F6iK6oefCbkJiA4/i6fnTHzM6H1kEA=="
    crossorigin=""></script>

  <!-- Load Esri Leaflet Vector from CDN -->
  <script src="https://unpkg.com/esri-leaflet-vector@4.0.0/dist/esri-leaflet-vector.js"
    integrity="sha512-EMt/tpooNkBOxxQy2SOE1HgzWbg9u1gI6mT23Wl0eBWTwN9nuaPtLAaX9irNocMrHf0XhRzT8B0vXQ/bzD0I0w=="
    crossorigin=""></script>

  <!-- Load Leaflet MarkerCluster and Esri Leaflet Cluster from CDN -->
  <link rel="stylesheet" type="text/css"
    href="https://unpkg.com/leaflet.markercluster@1.5.0/dist/MarkerCluster.Default.css"
    integrity="sha512-6ZCLMiYwTeli2rVh3XAPxy3YoR5fVxGdH/pz+KMCzRY2M65Emgkw00Yqmhh8qLGeYQ3LbVZGdmOX9KUjSKr0TA=="
    crossorigin="">
  <link rel="stylesheet" type="text/css" href="https://unpkg.com/leaflet.markercluster@1.5.0/dist/MarkerCluster.css"
    integrity="sha512-mQ77VzAakzdpWdgfL/lM1ksNy89uFgibRQANsNneSTMD/bj0Y/8+94XMwYhnbzx8eki2hrbPpDm0vD0CiT2lcg=="
    crossorigin="">
  <script src="https://unpkg.com/leaflet.markercluster@1.5.0/dist/leaflet.markercluster.js"
    integrity="sha512-pWPELjRaw2ZdoT0PDi7iRpRlk1XX3rtnfejJ/HwskyojpHei+9hKpwdphC4yssNt4FM0TjMQOmMrk6ZYSn274w=="
    crossorigin=""></script>
  <script src="https://unpkg.com/esri-leaflet-cluster@3.0.0/dist/esri-leaflet-cluster.js"
    integrity="sha512-XFCzSxay1bEwLt/pTNuKEw11WbMGlWUqSLMGUtsle2Zbddt2C5uf18w0HeHbc0NP9BTFy1Mzhab7Bkr+nxp34g=="
    crossorigin=""></script>

  <style>
    body { margin:0; padding:0; }
    #map { position: absolute; top:0; bottom:0; right:0; left:0; }
  </style>
</head>
<body>

<style>
  .cluster {
    background: #2d84c8;
    border-radius: 50%;
    text-align: center;
    color: white;
    font-weight: 700;
    border: 1px solid #2d84c8;
    font-family: monospace;
  }

  .cluster:before {
    content: ' ';
    position: absolute;
    border-radius: 50%;
    z-index: -1;
    top: 1px;
    left: 1px;
    right: 1px;
    bottom: 1px;
    border: 1px solid white;
  }

  .digits-1 {
    font-size: 14px;
    height: 28px;
    width: 28px;
    line-height: 28px;
    margin-top: -14px;
    margin-left: -14px;
  }

  .digits-2 {
    font-size: 16px;
    height: 34px;
    width: 34px;
    line-height: 35px;
    margin-top: -17px;
    margin-left: -17px;
  }

  .digits-2:before {
    border-width: 2px;
  }

  .digits-3 {
    font-size: 18px;
    height: 48px;
    width: 47px;
    line-height: 47px;
    border-width: 3px;
    margin-top: -24px;
    margin-left: -24px;
  }

  .digits-3:before {
    border-width: 3px;
  }

  .digits-4 {
    font-size: 18px;
    height: 58px;
    width: 58px;
    line-height: 57px;
    border-width: 4px;
    margin-top: -29px;
    margin-left: -29px;
  }

  .digits-4:before {
    border-width: 4px;
  }
</style>

<div id="map"></div>

<script>
  var map = L.map('map', {
    maxZoom: 18 // the clustering plugin needs some help understanding the map's maxZoom
  }).setView([0, 0], 2);

  L.esri.Vector.vectorBasemapLayer('ArcGIS:NavigationNight', {
    apikey: apiKey // Replace with your API key - https://developers.arcgis.com
  }).addTo(map);

  // create a new cluster layer (new syntax at 2.0.0)
  var earthquakes = L.esri.Cluster.featureLayer({
    url: 'https://sampleserver6.arcgisonline.com/arcgis/rest/services/Earthquakes_Since1970/MapServer/0',
    spiderfyOnMaxZoom: false,
    removeOutsideVisibleBounds: true,
    disableClusteringAtZoom: 8,
    // this function defines how the icons
    // representing clusters are created
    iconCreateFunction: function (cluster) {
      // get the number of items in the cluster
      var count = cluster.getChildCount();

      // figure out how many digits long the number is
      var digits = (count + '').length;

      // Return a new L.DivIcon with our classes so we can
      // style them with CSS. Take a look at the CSS in
      // the <head> to see these styles. You have to set
      // iconSize to null if you want to use CSS to set the
      // width and height.
      return L.divIcon({
        html: count,
        className: 'cluster digits-' + digits,
        iconSize: null
      });
    },
    // This function defines how individual markers
    // are created. You can see we are using the
    // value of the "magnitude" field to set the symbol
    pointToLayer: function (geojson, latlng) {
      var magnitude = (geojson.properties.magnitude);
      var earthquakeSymbol = '';

      if (!magnitude) {
        earthquakeSymbol = 'https://esri.github.io/esri-leaflet/img/earthquake-icon.png';
      } else if (magnitude <= 4.999) {
        earthquakeSymbol = 'https://esri.github.io/esri-leaflet/img/yellow-triangle.png';
      } else if (magnitude >= 5 && magnitude <= 6.999) {
        earthquakeSymbol = 'https://esri.github.io/esri-leaflet/img/orange-triangle.png';
      } else if (magnitude >= 7) {
        earthquakeSymbol = 'https://esri.github.io/esri-leaflet/img/red-triangle.png';
      }

      var mapIcon = L.icon({
        iconUrl: earthquakeSymbol,
        iconSize: [20, 20]
      });

      return L.marker(latlng, {
        icon: mapIcon
      });
    }
  }).addTo(map);

  earthquakes.bindPopup(function (layer) {
    return L.Util.template('Magnitude <strong>{magnitude}</strong> earthquake', layer.feature.properties);
  });
</script>

</body>
</html>
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