How to convert a relative or virtual path in an IIS server to the corresponding physical directory?

The Server.MapPath property maps the specified relative or virtual path to the corresponding physical directory on the server.

protected void Application_Start(Object sender, EventArgs e)
{
 StreamReader sr = null;
 XmlDocument xmldoc = new XmlDocument();
 try
 {
  sr = new StreamReader(Server.MapPath("./Data/content.xml"));
  xmldoc.LoadXml(sr.ReadToEnd());
  //.....
  
 }
 finally
 {
  if (sr != null)
  {
    sr.Close();
  }
 }
}