Displaying markers for local attractions on a Google map
First off, I find it helpful to use arrays instead of multiple variables. So, how about this:

var map = [], infoWindow = [];


Then, lets rename id map to map0. This will allow us to be clever with how we reference it :)

Now we refactor initialize to use the array and reduce repetition:

function initialize(){
   initMap(0, 51.5069999695, -0.142489999533);
   initMap(1, 40.79445,-74.01558);
   initMap(2 , 48.858001709, 2.29460000992);
}

function initMap(ndx, lat, lng){
   var feed = new google.maps.LatLng(lat, lng);

   map[ndx] = new google.maps.Map(document.getElementById('map'+ndx), {
      mapTypeId: google.maps.MapTypeId.ROADMAP,
      center: feed,
      zoom: 11
   });

   var request = {
      location: feed,
      radius: 5000
   };

   infoWindow[ndx] = new google.maps.InfoWindow();
   var service = new google.maps.places.PlacesService(map);
   service.search(request, callback);
}


Finally, lets refactor createMarker to use the arrays as well.

function callback(results, status) {
   if (status == google.maps.places.PlacesServiceStatus.OK) {
      for (var i = 0; i &lt; results.length; i++) {
         createMarker(0, results[i]);
         createMarker(1, results[i]);
         createMarker(2, results[i]);
      }
   }
}

function createMarker(ndx, place) {
   var marker = new google.maps.Marker({
      animation: google.maps.Animation.DROP,
      map: map[ndx],
      position: place.geometry.location
   });

   google.maps.event.addListener(marker, 'click', function() {
      infowindow[ndx].setContent(place.name);
      infowindow[ndx].open(map[ndx], this);
   });        
}

google.maps.event.addDomListener(window, 'load', initialize);


Finally, don't forget to rename map to map0

&lt;div id="map0" style="position:absolute; width: 290px; height: 300px;"&gt;&lt;/div&gt;
&lt;div id="map1" style="position:absolute; left:300px; width: 290px; height: 300px;"&gt;&lt;/div&gt;
&lt;div id="map2" style="position:absolute; left:600px; width: 290px; height: 300px;"&gt;&lt;/div&gt;