protected void Application_Start(object sender, EventArgs e)
{
    RegisterRoutes(RouteTable.Routes);
}
void RegisterRoutes(RouteCollection routes)
{
    routes.MapPageRoute(
        "HomeRoute",
        "Home",
        "~/Default.aspx"
    );
    routes.MapPageRoute(
        "SecondRoute",
        "Second",
        "~/Second.aspx"
    );
    routes.MapPageRoute(
        "ThirdRoute",
        "Third/{Name}",
        "~/Third.aspx"
    );
}

protected void Button2_Click(object sender, EventArgs e)
{
    //Response.Redirect("Third.aspx?Name=Pants");
   Response.Redirect(GetRouteUrl("ThirdRoute", new {Name = "Pants"}));
}