List<GLatLng> markersToShow = new ArrayList<GLatLng>();
// add some markers
GLatLng glatlng1 = new GLatLng(47.4915285, 8.2050407);
GMarkerOptions opts1 = new GMarkerOptions(map, glatlng1);
GMarker marker1 = new GMarker("marker1", opts1);
map.addOverlay(marker1);
GLatLng glatlng2 = new GLatLng(50.7706934, 2.2164129);
GMarkerOptions opts2 = new GMarkerOptions(map, glatlng2);
GMarker marker2 = new GMarker("marker2", opts2);
map.addOverlay(marker2);
GLatLng glatlng3 = new GLatLng(48.858859, 2.34706);
GMarkerOptions opts3 = new GMarkerOptions(map, glatlng3);
GMarker marker3 = new GMarker("marker3", opts3);
map.addOverlay(marker3);
// add them to the list of coordinates that we need in our viewport
markersToShow.add(glatlng1);
markersToShow.add(glatlng2);