Make users be able to add 2 markers on a map.

function addMarker(map) {
  var marker = new google.maps.Marker({
    position: map.getCenter(),
    map: map,
    title: 'Click to zoom'
  });

  google.maps.event.addListener(marker, 'click', function() {
    map.setZoom(8);
    map.setCenter(marker.getPosition());
  });
}