Google MapとMarker clusterの連動基本

index.html

<!-- 省略 -->
<script src="https://maps.googleapis.com/maps/api/js"></script>
<script src="markerclusterer_compiled.js"></script>
<script src="map.js"></script>

<!-- 省略 -->

<!--
markerclusterer_compiled.js
src -> https://github.com/googlemaps/js-marker-clusterer
-->

map.js

var mapCanvas = document.getElementById('map');
var mapOptions = {
  center: new google.maps.LatLng(緯度,経度)
};

var myMap = new google.maps.Map(mapCanvas, mapOptions);
var markers = [], marker, markerOptions;
var ary = [];  // 緯度経度の入った配列データを用意する
var i = 0;
var l = ary.length;

for (; i < l; i++) {
  markerOptions = {
    position: new google.maps.LatLng(ary[i][1], ary[i][0])
  };
  marker = new google.maps.Marker(markerOptions);
  markers.push(marker);
}

var markerCluster = new MarkerClusterer(myMap, markers);