function displayMapAndClick ()
    {
        var latlng    = new google.maps.LatLng (29.0167, 77.3833);
        var myOptions =
        {
            zoom:zm,
            center:latlng,
            mapTypeId:google.maps.MapTypeId.ROADMAP
        };

        map = new google.maps.Map (document.getElementById ("map"), myOptions);
        directionsDisplay.setMap (map);
    }

var mapOptions = {
  /* Initial zoom level */
  zoom: 8
  ...
};
map = new google.maps.Map(..., mapOptions);
/* Change zoom level to 12  */
map.setZoom(12);

...
map = new google.maps.Map(..., mapOptions);
/* Change zoom level to 12  */
google.maps.event.addListenerOnce(map, 'bounds_changed', function() {
  map.setZoom(12);
});