Symbol Layer

<!--
  示例：符号图层
  核心逻辑：symbol 图层绑定点位，text-size 按缩放插值，滑块再乘一个字号系数
  依赖：MapLibre GL JS 4 · jsDelivr CDN · demotiles 样式与字形
-->
<!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>符号图层</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.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;color:#16181d}
  .bar{flex:0 0 auto;display:flex;gap:12px;align-items:center;padding:8px 12px;
       background:#f6f7f9;border-bottom:1px solid #e3e6ea;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  .bar input[type=range]{width:120px}
  #map{flex:1 1 auto;min-height:0}
</style>
</head>
<body>
<div class="bar">
  <label>字号系数 <input id="scale" type="range" min="0.6" max="1.8" step="0.1" value="1"> <b id="scalev">1.0</b></label>
  <span>缩放 <b id="z">—</b></span>
  <span>标注用 Noto Sans Regular 字形</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.js"></script>
<script>
(function () {
  'use strict';

  if (typeof maplibregl === 'undefined') {
    document.body.innerHTML =
      '<div style="padding:24px;color:#b42318">MapLibre 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var cities = {
    type: 'FeatureCollection',
    features: [
      ['Beijing', 116.41, 39.90, 1],
      ['Shanghai', 121.47, 31.23, 1],
      ['Guangzhou', 113.26, 23.13, 1],
      ['Chengdu', 104.07, 30.67, 1],
      ['Wuhan', 114.31, 30.59, 1],
      ['Xian', 108.94, 34.34, 1],
      ['Harbin', 126.53, 45.80, 1],
      ['Kunming', 102.83, 24.88, 1],
      ['Lhasa', 91.14, 29.65, 1],
      ['Urumqi', 87.62, 43.82, 1]
    ].map(function (c) {
      return {
        type: 'Feature',
        properties: { name: c[0], rank: c[3] },
        geometry: { type: 'Point', coordinates: [c[1], c[2]] }
      };
    })
  };

  var map = new maplibregl.Map({
    container: 'map',
    style: 'https://demotiles.maplibre.org/style.json',
    center: [108.0, 34.0],
    zoom: 3,
    attributionControl: { compact: true, customAttribution: 'MapLibre demo tiles' }
  });

  map.addControl(new maplibregl.NavigationControl(), 'top-right');

  function sizeExpr(factor) {
    return ['*', ['interpolate', ['linear'], ['zoom'], 2, 10, 7, 17], factor];
  }

  map.on('load', function () {
    map.addSource('cities', { type: 'geojson', data: cities });

    map.addLayer({
      id: 'city-dot',
      type: 'circle',
      source: 'cities',
      paint: {
        'circle-radius': 4,
        'circle-color': '#1f5fd0',
        'circle-stroke-color': '#ffffff',
        'circle-stroke-width': 1.5
      }
    });

    map.addLayer({
      id: 'city-label',
      type: 'symbol',
      source: 'cities',
      layout: {
        'text-field': ['get', 'name'],
        'text-font': ['Noto Sans Regular'],
        'text-size': sizeExpr(1),
        'text-offset': [0, 1.2],
        'text-anchor': 'top',
        'text-allow-overlap': false
      },
      paint: {
        'text-color': '#14263d',
        'text-halo-color': '#ffffff',
        'text-halo-width': 1.6
      }
    });
  });

  document.getElementById('scale').addEventListener('input', function () {
    var v = parseFloat(this.value);
    document.getElementById('scalev').textContent = v.toFixed(1);
    if (map.getLayer('city-label')) {
      map.setLayoutProperty('city-label', 'text-size', sizeExpr(v));
    }
  });

  map.on('moveend', function () {
    document.getElementById('z').textContent = map.getZoom().toFixed(2);
  });

  map.on('error', function (e) {
    if (e.error) console.warn('地图错误：' + e.error.message);
  });
})();
</script>
</body>
</html>