住所からGoogle mapに2つのラベルを表示する – ソフトウェアエンジニアの技術ブログ：Software engineer tech blog

なんとなく、それらしいものができてきました。中心のポジションは、緯度経度の平均を取ってます。
あ、array_sum, countでできますね。
$lat_a = array_sum($lat)/count($lat);
$lng_a = array_sum($lng)/count($lng);

<?php

$resutaurant = array(
    "Brasserie de L'institut" => "東京都新宿区市谷船河原町15",
    "Le Mange-Tout" => '東京都新宿区納戸町22'
  );
function urlencode_rfc3986($str){
  return str_replace('%7E','~', rawurlencode($str));
}
$i = 0;
foreach($resutaurant as $name => $address){
  $encode_address = urlencode_rfc3986($address);

  $url = 'http://maps.google.com/maps/api/geocode/json?address='. $encode_address.'&sensor=false';
  $json = file_get_contents($url);
  $obj = json_decode($json,true);

  $lat[] = $obj["results"]["0"]["geometry"]["location"]["lat"];
  $lng[] = $obj["results"]["0"]["geometry"]["location"]["lng"];
  echo $name ." ".$address .'<br>';
  echo $lat[$i] ." " .$lng[$i]. "<br>";
  $rname[] = $name;
  $i++;
}

$lat_a = ($lat[0]+$lat[1])/2;
$lng_a = ($lng[0]+$lng[1])/2;


?>
<!DOCTYPE html>
<html>
  <head>
    <title>Simple Map</title>
    <meta name="viewport" content="initial-scale=1.0">
    <meta charset="utf-8">
    <style>
      #map {
        height: 50%;
        margin-top: 10px;
      }
      html, body {
        height: 100%;
        margin: 10px;
        padding: 0;
      }
    </style>
  </head>
  <body>
  	<div id="map"></div>
  	<script>
  	var map;
  	function initMap(){
      var position = {lat: <?php echo $lat_a; ?>, lng: <?php echo $lng_a; ?>};
  		map = new google.maps.Map(document.getElementById('map'),{
  			center: position,
  			zoom: 16
  		});

      var labels = ["<?php echo $rname&#91;0&#93;; ?>","<?php echo $rname&#91;1&#93;; ?>"];

      var markers = locations.map(function(location, i) {
          return new google.maps.Marker({
            position: location,
            label: labels[i]
          });
        });

      var markerCluster = new MarkerClusterer(map, markers,
            {imagePath: 'https://developers.google.com/maps/documentation/javascript/examples/markerclusterer/m'});
      }

    var locations = [
    {lat: <?php echo $lat&#91;0&#93;; ?>, lng: <?php echo $lng&#91;0&#93;; ?>},
    {lat: <?php echo $lat&#91;1&#93;; ?>, lng: <?php echo $lng&#91;1&#93;; ?>}
    ]
  	</script>
    <script src="https://developers.google.com/maps/documentation/javascript/examples/markerclusterer/markerclusterer.js">
    </script>
  	<script async defer
src = "https:maps.googleapis.com/maps/api/js?key=hogehogek&callback=initMap">
</script>
</body>
</html>