Cluster Graded

<!--
  示例：分级聚合
  要点：Cluster 要素用 get('features').length 分级配色，点击聚合点 fit 到簇范围
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>分级聚合</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e}
  .dot{display:inline-block;width:9px;height:9px;border-radius:50%;margin-right:4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span><i class="dot" style="background:#1f5fd0"></i>≤10</span>
  <span><i class="dot" style="background:#d97706"></i>≤30</span>
  <span><i class="dot" style="background:#c0392b"></i>&gt;30</span>
  <span>点击聚合点放大</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var seed = 8721;
  function rand() {
    seed = (seed * 1103515245 + 12345) % 2147483648;
    return seed / 2147483648;
  }

  /* 围绕三个商圈生成点位，形成疏密差异 */
  var centers = [
    [116.4106, 39.9147],
    [116.3800, 39.9005],
    [116.4300, 39.9250]
  ];

  var features = [];
  centers.forEach(function (c, idx) {
    var n = 40 + idx * 30;
    for (var i = 0; i < n; i++) {
      features.push(new ol.Feature({
        geometry: new ol.geom.Point(ol.proj.fromLonLat([
          c[0] + (rand() - 0.5) * 0.02,
          c[1] + (rand() - 0.5) * 0.016
        ]))
      }));
    }
  });

  var clusterSource = new ol.source.Cluster({
    distance: 38,
    source: new ol.source.Vector({ features: features })
  });

  var layer = new ol.layer.Vector({ source: clusterSource });

  function clusterStyle(feature) {
    var items = feature.get('features');
    var size = items ? items.length : 1;

    var color = '#1f5fd0';
    if (size > 30) {
      color = '#c0392b';
    } else if (size > 10) {
      color = '#d97706';
    }

    var radius = Math.min(24, 8 + Math.log(size) * 4);

    return new ol.style.Style({
      image: new ol.style.Circle({
        radius: radius,
        fill: new ol.style.Fill({ color: color }),
        stroke: new ol.style.Stroke({ color: '#ffffff', width: 2 })
      }),
      text: new ol.style.Text({
        text: size > 1 ? String(size) : '',
        font: '600 12px sans-serif',
        fill: new ol.style.Fill({ color: '#ffffff' })
      })
    });
  }

  layer.setStyle(clusterStyle);

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }), layer],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.405, 39.912]),
      zoom: 12
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  map.on('singleclick', function (evt) {
    var hit = map.forEachFeatureAtPixel(evt.pixel, function (f) {
      return f;
    });

    if (!hit) {
      return;
    }

    var members = hit.get('features');
    if (!members || members.length < 2) {
      return;
    }

    var extent = ol.extent.createEmpty();
    members.forEach(function (f) {
      ol.extent.extend(extent, f.getGeometry().getExtent());
    });

    map.getView().fit(extent, {
      padding: [60, 60, 60, 60],
      duration: 400,
      maxZoom: 16
    });
  });
})();
</script>
</body>
</html>