Traçando rota entre dois pontos com Google Maps API

 var directionsDisplay;
 var directionsService = new google.maps.DirectionsService();
 var map;

 function initialize() {
  directionsDisplay = new google.maps.DirectionsRenderer();
  var center = new google.maps.LatLng(-8.288642,-35.031128);

  var mapOptions = {
    zoom:18,
    mapTypeId: google.maps.MapTypeId.ROADMAP,
    center: center
   }

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

 
 function calcRoute() {
  var start = '-8.288642,-35.031128';
  var end = '-8.288300,-35.029371';
  var request = {
    origin: start,
    destination: end,
    travelMode: google.maps.TravelMode.WALKING 
   };

  directionsService.route(request, function(result, status) {
   if (status == google.maps.DirectionsStatus.OK) {
    directionsDisplay.setDirections(result);
   }
  });
 }