整合并直观呈现多个数据源

概述

本教程介绍了如何在 Google 地图上显示来自多个来源的数据。例如，下面的分级统计图使用两个不同的来源突出显示美国各州，并显示特定州的具体数据。

该地图使用 GeoJSON 文件中的数据来显示用于定义美国各州边界的多边形。此外，它还可以在地图上显示各州的对应数据，这些数据来自对 US Census API 的模拟查询。

从控件下拉菜单中选择数据类别即可更新地图上的多边形。您还可以将鼠标悬停在州多边形上，在地图上的数据框控件中查看特定州的具体信息。

以下示例显示了创建此地图所需的完整代码。

TypeScript

const mapStyle: google.maps.MapTypeStyle[] = [
  {
    stylers: [{ visibility: "off" }],
  },
  {
    featureType: "landscape",
    elementType: "geometry",
    stylers: [{ visibility: "on" }, { color: "#fcfcfc" }],
  },
  {
    featureType: "water",
    elementType: "geometry",
    stylers: [{ visibility: "on" }, { color: "#bfd4ff" }],
  },
];
let map: google.maps.Map;

let censusMin = Number.MAX_VALUE,
  censusMax = -Number.MAX_VALUE;

function initMap(): void {
  // load the map
  map = new google.maps.Map(document.getElementById("map") as HTMLElement, {
    center: { lat: 40, lng: -100 },
    zoom: 4,
    styles: mapStyle,
  });

  // set up the style rules and events for google.maps.Data
  map.data.setStyle(styleFeature);
  map.data.addListener("mouseover", mouseInToRegion);
  map.data.addListener("mouseout", mouseOutOfRegion);

  // wire up the button
  const selectBox = document.getElementById(
    "census-variable"
  ) as HTMLSelectElement;

  google.maps.event.addDomListener(selectBox, "change", () => {
    clearCensusData();
    loadCensusData(selectBox.options[selectBox.selectedIndex].value);
  });

  // state polygons only need to be loaded once, do them now
  loadMapShapes();
}

/** Loads the state boundary polygons from a GeoJSON source. */
function loadMapShapes() {
  // load US state outline polygons from a GeoJson file
  map.data.loadGeoJson(
    "https://storage.googleapis.com/mapsdevsite/json/states.js",
    { idPropertyName: "STATE" }
  );

  // wait for the request to complete by listening for the first feature to be
  // added
  google.maps.event.addListenerOnce(map.data, "addfeature", () => {
    google.maps.event.trigger(
      document.getElementById("census-variable") as HTMLElement,
      "change"
    );
  });
}

/**
 * Loads the census data from a simulated API call to the US Census API.
 *
 * @param {string} variable
 */
function loadCensusData(variable: string) {
  // load the requested variable from the census API (using local copies)
  const xhr = new XMLHttpRequest();

  xhr.open("GET", variable + ".json");

  xhr.onload = function () {
    const censusData = JSON.parse(xhr.responseText) as any;

    censusData.shift(); // the first row contains column names
    censusData.forEach((row: string) => {
      const censusVariable = parseFloat(row[0]);
      const stateId = row[1];

      // keep track of min and max values
      if (censusVariable < censusMin) {
        censusMin = censusVariable;
      }

      if (censusVariable > censusMax) {
        censusMax = censusVariable;
      }

      const state = map.data.getFeatureById(stateId);

      // update the existing row with the new data
      if (state) {
        state.setProperty("census_variable", censusVariable);
      }
    });

    // update and display the legend
    (document.getElementById("census-min") as HTMLElement).textContent =
      censusMin.toLocaleString();
    (document.getElementById("census-max") as HTMLElement).textContent =
      censusMax.toLocaleString();
  };

  xhr.send();
}

/** Removes census data from each shape on the map and resets the UI. */
function clearCensusData() {
  censusMin = Number.MAX_VALUE;
  censusMax = -Number.MAX_VALUE;
  map.data.forEach((row) => {
    row.setProperty("census_variable", undefined);
  });
  (document.getElementById("data-box") as HTMLElement).style.display = "none";
  (document.getElementById("data-caret") as HTMLElement).style.display = "none";
}

/**
 * Applies a gradient style based on the 'census_variable' column.
 * This is the callback passed to data.setStyle() and is called for each row in
 * the data set.  Check out the docs for Data.StylingFunction.
 *
 * @param {google.maps.Data.Feature} feature
 */
function styleFeature(feature: google.maps.Data.Feature) {
  const low = [5, 69, 54]; // color of smallest datum
  const high = [151, 83, 34]; // color of largest datum

  let censusVariable = feature.getProperty("census_variable") as number;

  // delta represents where the value sits between the min and max
  const delta =
    (censusVariable - censusMin) /
    (censusMax - censusMin);

  const color: number[] = [];

  for (let i = 0; i < 3; i++) {
    // calculate an integer color based on the delta
    color.push((high[i] - low[i]) * delta + low[i]);
  }

  // determine whether to show this shape or not
  let showRow = true;

  if (
    censusVariable == null ||
    isNaN(censusVariable)
  ) {
    showRow = false;
  }

  let outlineWeight = 0.5,
    zIndex = 1;

  if (feature.getProperty("state") === "hover") {
    outlineWeight = zIndex = 2;
  }

  return {
    strokeWeight: outlineWeight,
    strokeColor: "#fff",
    zIndex: zIndex,
    fillColor: "hsl(" + color[0] + "," + color[1] + "%," + color[2] + "%)",
    fillOpacity: 0.75,
    visible: showRow,
  };
}

/**
 * Responds to the mouse-in event on a map shape (state).
 *
 * @param {?google.maps.MapMouseEvent} e
 */
function mouseInToRegion(e: any) {
  // set the hover state so the setStyle function can change the border
  e.feature.setProperty("state", "hover");

  const percent =
    ((e.feature.getProperty("census_variable") - censusMin) /
      (censusMax - censusMin)) *
    100;

  // update the label
  (document.getElementById("data-label") as HTMLElement).textContent =
    e.feature.getProperty("NAME");
  (document.getElementById("data-value") as HTMLElement).textContent = e.feature
    .getProperty("census_variable")
    .toLocaleString();
  (document.getElementById("data-box") as HTMLElement).style.display = "block";
  (document.getElementById("data-caret") as HTMLElement).style.display =
    "block";
  (document.getElementById("data-caret") as HTMLElement).style.paddingLeft =
    percent + "%";
}

/**
 * Responds to the mouse-out event on a map shape (state).
 *
 */
function mouseOutOfRegion(e: any) {
  // reset the hover state, returning the border to normal
  e.feature.setProperty("state", "normal");
}

declare global {
  interface Window {
    initMap: () => void;
  }
}
window.initMap = initMap;
index.ts

JavaScript

const mapStyle = [
  {
    stylers: [{ visibility: "off" }],
  },
  {
    featureType: "landscape",
    elementType: "geometry",
    stylers: [{ visibility: "on" }, { color: "#fcfcfc" }],
  },
  {
    featureType: "water",
    elementType: "geometry",
    stylers: [{ visibility: "on" }, { color: "#bfd4ff" }],
  },
];
let map;
let censusMin = Number.MAX_VALUE,
  censusMax = -Number.MAX_VALUE;

function initMap() {
  // load the map
  map = new google.maps.Map(document.getElementById("map"), {
    center: { lat: 40, lng: -100 },
    zoom: 4,
    styles: mapStyle,
  });
  // set up the style rules and events for google.maps.Data
  map.data.setStyle(styleFeature);
  map.data.addListener("mouseover", mouseInToRegion);
  map.data.addListener("mouseout", mouseOutOfRegion);

  // wire up the button
  const selectBox = document.getElementById("census-variable");

  google.maps.event.addDomListener(selectBox, "change", () => {
    clearCensusData();
    loadCensusData(selectBox.options[selectBox.selectedIndex].value);
  });
  // state polygons only need to be loaded once, do them now
  loadMapShapes();
}

/** Loads the state boundary polygons from a GeoJSON source. */
function loadMapShapes() {
  // load US state outline polygons from a GeoJson file
  map.data.loadGeoJson(
    "https://storage.googleapis.com/mapsdevsite/json/states.js",
    { idPropertyName: "STATE" },
  );
  // wait for the request to complete by listening for the first feature to be
  // added
  google.maps.event.addListenerOnce(map.data, "addfeature", () => {
    google.maps.event.trigger(
      document.getElementById("census-variable"),
      "change",
    );
  });
}

/**
 * Loads the census data from a simulated API call to the US Census API.
 *
 * @param {string} variable
 */
function loadCensusData(variable) {
  // load the requested variable from the census API (using local copies)
  const xhr = new XMLHttpRequest();

  xhr.open("GET", variable + ".json");
  xhr.onload = function () {
    const censusData = JSON.parse(xhr.responseText);

    censusData.shift(); // the first row contains column names
    censusData.forEach((row) => {
      const censusVariable = parseFloat(row[0]);
      const stateId = row[1];

      // keep track of min and max values
      if (censusVariable < censusMin) {
        censusMin = censusVariable;
      }

      if (censusVariable > censusMax) {
        censusMax = censusVariable;
      }

      const state = map.data.getFeatureById(stateId);

      // update the existing row with the new data
      if (state) {
        state.setProperty("census_variable", censusVariable);
      }
    });
    // update and display the legend
    document.getElementById("census-min").textContent =
      censusMin.toLocaleString();
    document.getElementById("census-max").textContent =
      censusMax.toLocaleString();
  };

  xhr.send();
}

/** Removes census data from each shape on the map and resets the UI. */
function clearCensusData() {
  censusMin = Number.MAX_VALUE;
  censusMax = -Number.MAX_VALUE;
  map.data.forEach((row) => {
    row.setProperty("census_variable", undefined);
  });
  document.getElementById("data-box").style.display = "none";
  document.getElementById("data-caret").style.display = "none";
}

/**
 * Applies a gradient style based on the 'census_variable' column.
 * This is the callback passed to data.setStyle() and is called for each row in
 * the data set.  Check out the docs for Data.StylingFunction.
 *
 * @param {google.maps.Data.Feature} feature
 */
function styleFeature(feature) {
  const low = [5, 69, 54]; // color of smallest datum
  const high = [151, 83, 34]; // color of largest datum
  let censusVariable = feature.getProperty("census_variable");
  // delta represents where the value sits between the min and max
  const delta = (censusVariable - censusMin) / (censusMax - censusMin);
  const color = [];

  for (let i = 0; i < 3; i++) {
    // calculate an integer color based on the delta
    color.push((high[i] - low[i]) * delta + low[i]);
  }

  // determine whether to show this shape or not
  let showRow = true;

  if (censusVariable == null || isNaN(censusVariable)) {
    showRow = false;
  }

  let outlineWeight = 0.5,
    zIndex = 1;

  if (feature.getProperty("state") === "hover") {
    outlineWeight = zIndex = 2;
  }
  return {
    strokeWeight: outlineWeight,
    strokeColor: "#fff",
    zIndex: zIndex,
    fillColor: "hsl(" + color[0] + "," + color[1] + "%," + color[2] + "%)",
    fillOpacity: 0.75,
    visible: showRow,
  };
}

/**
 * Responds to the mouse-in event on a map shape (state).
 *
 * @param {?google.maps.MapMouseEvent} e
 */
function mouseInToRegion(e) {
  // set the hover state so the setStyle function can change the border
  e.feature.setProperty("state", "hover");

  const percent =
    ((e.feature.getProperty("census_variable") - censusMin) /
      (censusMax - censusMin)) *
    100;

  // update the label
  document.getElementById("data-label").textContent =
    e.feature.getProperty("NAME");
  document.getElementById("data-value").textContent = e.feature
    .getProperty("census_variable")
    .toLocaleString();
  document.getElementById("data-box").style.display = "block";
  document.getElementById("data-caret").style.display = "block";
  document.getElementById("data-caret").style.paddingLeft = percent + "%";
}

/**
 * Responds to the mouse-out event on a map shape (state).
 *
 */
function mouseOutOfRegion(e) {
  // reset the hover state, returning the border to normal
  e.feature.setProperty("state", "normal");
}

window.initMap = initMap;
index.js

CSS

html,
body,
#map {
  height: 100%;
  margin: 0;
  padding: 0;
  overflow: hidden;
}

.nicebox {
  position: absolute;
  text-align: center;
  font-family: "Roboto", "Arial", sans-serif;
  font-size: 13px;
  z-index: 5;
  box-shadow: 0 4px 6px -4px #333;
  padding: 5px 10px;
  background: rgb(255, 255, 255);
  background: linear-gradient(to bottom, rgb(255, 255, 255) 0%, rgb(245, 245, 245) 100%);
  border: rgb(229, 229, 229) 1px solid;
}

#controls {
  top: 10px;
  left: 110px;
  width: 360px;
  height: 45px;
}

#data-box {
  top: 10px;
  left: 500px;
  height: 45px;
  line-height: 45px;
  display: none;
}

#census-variable {
  width: 360px;
  height: 20px;
}

#legend {
  display: flex;
  display: -webkit-box;
  padding-top: 7px;
}

.color-key {
  background: linear-gradient(to right, hsl(5, 69%, 54%) 0%, hsl(29, 71%, 51%) 17%, hsl(54, 74%, 47%) 33%, hsl(78, 76%, 44%) 50%, hsl(102, 78%, 41%) 67%, hsl(127, 81%, 37%) 83%, hsl(151, 83%, 34%) 100%);
  flex: 1;
  -webkit-box-flex: 1;
  margin: 0 5px;
  text-align: left;
  font-size: 1em;
  line-height: 1em;
}

#data-value {
  font-size: 2em;
  font-weight: bold;
}

#data-label {
  font-size: 2em;
  font-weight: normal;
  padding-right: 10px;
}

#data-label:after {
  content: ":";
}

#data-caret {
  margin-left: -5px;
  display: none;
  font-size: 14px;
  width: 14px;
}

style.css

HTML

<html>
  <head>
    <title>Mashups with google.maps.Data</title>

    <link rel="stylesheet" type="text/css" href="./style.css" />
    <script type="module" src="./index.js"></script>
  </head>
  <body>
    <div id="controls" class="nicebox">
      <div>
        <select id="census-variable">
          <option
            value="https://storage.googleapis.com/mapsdevsite/json/DP02_0066PE"
          >
            Percent of population over 25 that completed high school
          </option>
          <option
            value="https://storage.googleapis.com/mapsdevsite/json/DP05_0017E"
          >
            Median age
          </option>
          <option
            value="https://storage.googleapis.com/mapsdevsite/json/DP05_0001E"
          >
            Total population
          </option>
          <option
            value="https://storage.googleapis.com/mapsdevsite/json/DP02_0016E"
          >
            Average family size
          </option>
          <option
            value="https://storage.googleapis.com/mapsdevsite/json/DP03_0088E"
          >
            Per-capita income
          </option>
        </select>
      </div>
      <div id="legend">
        <div id="census-min">min</div>
        <div class="color-key"><span id="data-caret">&#x25c6;</span></div>
        <div id="census-max">max</div>
      </div>
    </div>
    <div id="data-box" class="nicebox">
      <label id="data-label" for="data-value"></label>
      <span id="data-value"></span>
    </div>
    <div id="map"></div>

    <!-- 
      The `defer` attribute causes the script to execute after the full HTML
      document has been parsed. For non-blocking uses, avoiding race conditions,
      and consistent behavior across browsers, consider loading using Promises. See
      https://developers.google.com/maps/documentation/javascript/load-maps-js-api
      for more information.
      -->
    <script
      src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
      defer
    ></script>
  </body>
</html>
index.html

试用示例

入门指南

您可以使用本教程中的代码开发此分级统计图的自有版本。为此，请首先在文本编辑器中创建一个新文件并将其另存为 index.html。

请阅读接下来的各个部分，了解可添加到该文件中的代码。

创建基本地图

本部分介绍了用于设置基本地图的代码。这可能与您开始使用 Maps JavaScript API 时创建地图的方式类似。

请将下面的代码复制到 index.html 文件中。这段代码会加载 Maps JavaScript API，还会让地图以全屏方式显示。 

<!DOCTYPE html>
<html>
  <head>
  <meta charset="utf-8">
      <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
      <title>Mashups with google.maps.Data</title>
      <style>
        #map {
          height: 100%;
        }
        /* Optional: Makes the sample page fill the window. */
        html, body {
          height: 100%;
          margin: 0;
          padding: 0;
        }
      </style>
  </head>
  <body>
    <div id="map"></div>
    <script>
      function initMap() {

        // load the map
        map = new google.maps.Map(document.getElementById('map'), {
          center: {lat: 40, lng: -100},
          zoom: 4,
          styles: mapStyle
        });

        var mapStyle = [{
          'featureType': 'all',
          'elementType': 'all',
          'stylers': [{'visibility': 'off'}]
        }, {
          'featureType': 'landscape',
          'elementType': 'geometry',
          'stylers': [{'visibility': 'on'}, {'color': '#fcfcfc'}]
        }, {
          'featureType': 'water',
          'elementType': 'labels',
          'stylers': [{'visibility': 'off'}]
        }, {
          'featureType': 'water',
          'elementType': 'geometry',
          'stylers': [{'visibility': 'on'}, {'hue': '#5f94ff'}, {'lightness': 60}]
        }];
      }

    </script>
    <script defer
        src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap">
    </script>
  </body>
</html>

第一个脚本标记中的代码是程序运行的起点，这段代码创建了一个名为 initMap 的函数来初始化地图对象。

上述代码中的样式器 (stylers) 将地图上所有 featureTypes（例如道路、地图注点、景观、行政区）及其所有 elementTypes 的可见性都设为关闭。如需查看 featureType 和 elementType 的所有可用值的列表，请参阅 JSON 样式参考。

请点击代码示例中的 YOUR_API_KEY，或按照相关说明获取 API 密钥。将 YOUR_API_KEY 替换为您应用的 API 密钥。API 完全加载后，以下脚本标记中的回调参数会执行 HTML 文件中的 initMap() 函数。 

<script> defer
    src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap"
</script>

创建地图控件并设置其样式

下面的代码会在地图上创建以下控件：

  • 一个带有下拉菜单的控件，其中包含 5 个不同的数据选项。
  • 一个地图图例。
  • 一个用于显示特定州的具体信息的数据框，会在您将鼠标悬停在多边形上时显示。
<div id="controls" class="nicebox">
  <div>
  <select id="census-variable">
    <option value="https://storage.googleapis.com/mapsdevsite/json/DP02_0066PE">Percent of population over 25 that completed high
    school</option>
    <option value="https://storage.googleapis.com/mapsdevsite/json/DP05_0017E">Median age</option>
    <option value="https://storage.googleapis.com/mapsdevsite/json/DP05_0001E">Total population</option>
    <option value="https://storage.googleapis.com/mapsdevsite/json/DP02_0016E">Average family size</option>
    <option value="https://storage.googleapis.com/mapsdevsite/json/DP03_0088E">Per-capita income</option>
  </select>
  </div>
  <div id="legend">
    <div id="census-min">min</div>
    <div class="color-key"><span id="data-caret">&#x25c6;</span></div>
    <div id="census-max">max</div>
  </div>
</div>
<div id="data-box" class="nicebox">
  <label id="data-label" for="data-value"></label>
  <span id="data-value"></span>
</div>

使用 style 标记内的以下代码设置地图控件的样式。 

<style>
  html, body, #map { height: 100%; margin: 0; padding: 0; overflow: hidden; }
    .nicebox {
      position: absolute;
      text-align: center;
      font-family: "Roboto", "Arial", sans-serif;
      font-size: 13px;
      z-index: 5;
      box-shadow: 0 4px 6px -4px #333;
      padding: 5px 10px;
      background: rgb(255,255,255);
      background: linear-gradient(to bottom,rgba(255,255,255,1) 0%,rgba(245,245,245,1) 100%);
      border: rgb(229, 229, 229) 1px solid;
    }
    #controls {
      top: 10px;
      left: 110px;
      width: 360px;
      height: 45px;
    }
    #data-box {
      top: 10px;
      left: 500px;
      height: 45px;
      line-height: 45px;
      display: none;
    }
    #census-variable {
      width: 360px;
      height: 20px;
    }
    #legend { display: flex; display: -webkit-box; padding-top: 7px }
    .color-key {
      background: linear-gradient(to right,
        hsl(5, 69%, 54%) 0%,
        hsl(29, 71%, 51%) 17%,
        hsl(54, 74%, 47%) 33%,
        hsl(78, 76%, 44%) 50%,
        hsl(102, 78%, 41%) 67%,
        hsl(127, 81%, 37%) 83%,
        hsl(151, 83%, 34%) 100%);
      flex: 1;
      -webkit-box-flex: 1;
      margin: 0 5px;
      text-align: left;
      font-size: 1.0em;
      line-height: 1.0em;
    }
    #data-value { font-size: 2.0em; font-weight: bold }
    #data-label { font-size: 2.0em; font-weight: normal; padding-right: 10px; }
    #data-label:after { content: ':' }
    #data-caret { margin-left: -5px; display: none; font-size: 14px; width: 14px}
</style>

从 US Census API 导入数据

以下代码会向美国普查局查询美国各州的最新人口普查数据，并以 JSON 格式接收这些数据。 

function loadCensusData(variable) {
// load the requested variable from the census API
var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://api.census.gov/data/2012/acs5/profile?get=' +
  variable + '&for=state:*&key=YOUR_API_KEY');
        xhr.onload = function() {
          var censusData = JSON.parse(xhr.responseText);
          censusData.shift(); // the first row contains column names
          censusData.forEach(function(row) {
            var censusVariable = parseFloat(row[0]);
            var stateId = row[1];

            // keep track of min and max values
            if (censusVariable < censusMin) {
              censusMin = censusVariable;
            }
            if (censusVariable > censusMax) {
              censusMax = censusVariable;
            }

            // update the existing row with the new data
            map.data
              .getFeatureById(stateId)
              .setProperty('census_variable', censusVariable);
          });

          // update and display the legend
          document.getElementById('census-min').textContent =
              censusMin.toLocaleString();
          document.getElementById('census-max').textContent =
              censusMax.toLocaleString();
        };
        xhr.send();
}

设置数据样式

以下代码根据人口普查数据值，通过向数据集内的各个多边形应用渐变来创建分级统计图。您可以使用 Data.StyleOptions 对象或返回 Data.StyleOptions 对象的函数设置数据样式。 

// set up the style rules and events for google.maps.Data
map.data.setStyle(styleFeature);

      function styleFeature(feature) {
        var low = [5, 69, 54];  // color of smallest datum
        var high = [151, 83, 34];   // color of largest datum

        // delta represents where the value sits between the min and max
        var delta = (feature.getProperty('census_variable') - censusMin) /
            (censusMax - censusMin);

        var color = [];
        for (var i = 0; i < 3; i++) {
          // calculate an integer color based on the delta
          color[i] = (high[i] - low[i]) * delta + low[i];
        }

        // determine whether to show this shape or not
        var showRow = true;
        if (feature.getProperty('census_variable') == null ||
            isNaN(feature.getProperty('census_variable'))) {
          showRow = false;
        }

        var outlineWeight = 0.5, zIndex = 1;
        if (feature.getProperty('state') === 'hover') {
          outlineWeight = zIndex = 2;
        }

        return {
          strokeWeight: outlineWeight,
          strokeColor: '#fff',
          zIndex: zIndex,
          fillColor: 'hsl(' + color[0] + ',' + color[1] + '%,' + color[2] + '%)',
          fillOpacity: 0.75,
          visible: showRow
        };
      }

除了为多边形着色之外，以下代码还会通过添加用于响应鼠标活动的事件来创建互动元素。将鼠标悬停在多边形上可突出显示州边界，同时还可更新地图上的数据框控件。 

// set up the style rules and events for google.maps.Data
map.data.addListener('mouseover', mouseInToRegion);
map.data.addListener('mouseout', mouseOutOfRegion);

      /**
       * Responds to the mouse-in event on a map shape (state).
       *
       * @param {?google.maps.MapMouseEvent} e
       */
      function mouseInToRegion(e) {
        // set the hover state so the setStyle function can change the border
        e.feature.setProperty('state', 'hover');

        var percent = (e.feature.getProperty('census_variable') - censusMin) /
            (censusMax - censusMin) * 100;

        // update the label
        document.getElementById('data-label').textContent =
            e.feature.getProperty('NAME');
        document.getElementById('data-value').textContent =
            e.feature.getProperty('census_variable').toLocaleString();
        document.getElementById('data-box').style.display = 'block';
        document.getElementById('data-caret').style.display = 'block';
        document.getElementById('data-caret').style.paddingLeft = percent + '%';
      }

      /**
       * Responds to the mouse-out event on a map shape (state).
       *
       * @param {?google.maps.MapMouseEvent} e
       */
      function mouseOutOfRegion(e) {
        // reset the hover state, returning the border to normal
        e.feature.setProperty('state', 'normal');
      }

加载州边界多边形

请在整个 initMap 函数后面添加以下代码。loadMapShapes 函数使用 loadGeoJson 方法从 GeoJSON 文件加载美国各州边界的多边形。 

/** Loads the state boundary polygons from a GeoJSON source. */
function loadMapShapes() {
  // load US state outline polygons from a GeoJSON file
  map.data.loadGeoJson('https://storage.googleapis.com/mapsdevsite/json/states.js', { idPropertyName: 'STATE' });

将下面这行代码添加到 initMap 函数的末尾。 

  // state polygons only need to be loaded once, do them now
  loadMapShapes();

从地图控件下拉菜单中选择数据源选项时，地图会向 US Census Data API 查询指定变量。为了将人口普查数据与形状数据关联起来，上述代码会将 idPropertyName 设置为“STATE”，这是人口普查数据与 GeoJson 属性所共有的键。

更多信息

此演示使用的是 Census Bureau Data API，但未获得美国普查局的背书或认证。