function showLayer(id) {
		  document.getElementById(id).style.visibility = 'visible';
		}

		function hideLayer(id) {
		  document.getElementById(id).style.visibility = 'hidden';
		}
		
		function toggleLayer(id) {
		  var v = document.getElementById(id).style.visibility;
			if(v == 'hidden') {
					 showLayer(id);
			} else {
					 hideLayer(id);
			}
		}