Aquí está la documentación para MarkerClusterer for Google Maps V3
ejemplos de pago y envío MarkerClusterer for Google Maps V3 Sample Codes
Se puede agrupar sus marcadores en una forma que es más fácil de ver.
Aquí es un ejemplo del uso MarkerClusterer JSFiddle Demo.
var map = null;
var markerArray = []; //create a global array to store markers
var myPoints = [[43.65654, -79.90138, 'ABC'],[43.91892, -78.89231, 'DEF'],[43.82589, -79.10040, 'GHA']]; //create global array to store points
function initialize() {
var myOptions = {
zoom: 8,
center: new google.maps.LatLng(43.907787, -79.359741),
mapTypeControl: true,
mapTypeControlOptions: {
style: google.maps.MapTypeControlStyle.DROPDOWN_MENU
},
navigationControl: true,
mapTypeId: google.maps.MapTypeId.ROADMAP
}
map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
var mcOptions = {
gridSize: 50,
maxZoom: 15
};
var mc = new MarkerClusterer(map, [], mcOptions);
google.maps.event.addListener(map, 'click', function() {
infowindow.close();
});
// Add markers to the map
// Set up markers based on the number of elements within the myPoints array
for(var i=0; i<myPoints.length; i++){
createMarker(new google.maps.LatLng(myPoints[i][0], myPoints[i][1]), myPoints[i][2]);
}
mc.addMarkers(markerArray , true);
}
var infowindow = new google.maps.InfoWindow({
size: new google.maps.Size(150, 50)
});
function createMarker(latlng, html) {
var contentString = html;
var marker = new google.maps.Marker({
position: latlng,
map: map,
icon: 'http://www.kjftw.com/sandbox/gmap/images/icons/numeric/red10.png',
zIndex: Math.round(latlng.lat() * -100000) << 5
});
marker.setAnimation(google.maps.Animation.BOUNCE);
google.maps.event.addListener(marker, 'click', function() {
infowindow.setContent(contentString);
infowindow.open(map, marker);
});
markerArray.push(marker); //push local var marker into global array
}
window.onload = initialize;
Captura de pantalla de lo que parece agrupan:

Tal vez esta pregunta se relaciona con la suya: http://stackoverflow.com/q/5441979/675065 – Alp