1_DrawPathiOS_MarkOnMap.cs

//Code snippet to mark source and destination points
Location SourceLocation{get;set;}
Location DestinationLocation{get;set;}
//mark source point
strGeoCodeURL =string.Format ("https://maps.googleapis.com/maps/api/geocode/json?address={0}&key={1}",strSource,"ApiKeygeoeshere");
string strHttpResponse= await FnHttpRequest (strGeoCodeURL);
GeoCodeJSONClass objGeoCodeJSONClass = JsonConvert.DeserializeObject<GeoCodeJSONClass> (strHttpResponse);
//find GeoCodeJSONClass below in this page
if(objGeoCodeJSONClass!=null && objGeoCodeJSONClass.status=="OK")
{
	SourceLocation=new Location(){lat=objGeoCodeJSONClass.results[0].geometry.location.lat,lng=objGeoCodeJSONClass.results[0].geometry.location.lng};
	MarkOnMap (SourceLocation,"Start",UIImage.FromBundle("Images/MarkerSource"),false); 
}
//mark destination point
strGeoCodeURL =string.Format ("https://maps.googleapis.com/maps/api/geocode/json?address={0}&key={1}",strDestination,"apiKeygeoeshere");
string strHttpResponse = await FnHttpRequest ( strGeoCodeURL );
var objGeoCodeJSONClass = JsonConvert.DeserializeObject<GeoCodeJSONClass> (strHttpResponse);
if ( objGeoCodeJSONClass != null && objGeoCodeJSONClass.status == "OK" )
{
	DestinationLocation = new Location () { lat = objGeoCodeJSONClass.results [0].geometry.location.lat, lng = objGeoCodeJSONClass.results [0].geometry.location.lng };
	MarkOnMap ( DestinationLocation , "End" , UIImage.FromBundle ( "Images/MarkerDest" ) , false );
}
void MarkOnMap(Location location,string strTitle,UIImage imgIcon,bool isFlat)
{ 
	var marker = new Marker ();
	marker.Flat = isFlat;
	marker.Position = new CLLocationCoordinate2D ( location.lat , location.lng );
	marker.Map = mapView;
	marker.Title = strTitle;
	marker.Icon=imgIcon;
	marker.Draggable=false;
	marker.AppearAnimation=MarkerAnimation.Pop;  
}

FnHttpRequest.cs

//HttpWebRequest common method
static async Task<string> FnHttpRequest(string strURL)
{
	WebClient client = new WebClient ();
	string strResult;
	try
	{
		strResult=await client.DownloadStringTaskAsync (new Uri(strURL));
	}
	catch
	{
		strResult="Exception";
	}
	finally
	{
		client.Dispose ();
		client = null;
	}
	return strResult;
}