title: How can I change marker position eventually in google maps api?
body: <p>I have a problem with google maps api, when I change the marker position constantly, this leave a trace on map and I need move the marker without leaving a trace. 
  I actually get the latitude and the longitude from a database in firebase and need represent the route of a car.</p>
  
  <pre><code>var mapOptions = {
  
   center: new google.maps.LatLng(20.615977, -103.339358), 
   zoom: 12
  
  };
  
  var map = new google.maps.Map(document.getElementById("map"), mapOptions);    
  
  firebase.database().ref('route').on('value', function(data) {
  
  var start = new google.maps.Marker({
      position: {lat: latitud, lng: longitud}, 
      map: map,
      icon: '../icon/car.png'
  });
  
  var myLatlng = new google.maps.LatLng(data.val().latitude, data.val().longitude);
  
  start.setPosition(myLatlng);
  start.setMap(map);   
  
  });
  </code></pre>