<!--
// determine browser data object model (DOM) and build object string based on DOM
var isNav,isIE,isDOM;
var coll = "";
var styleObj = "";
//test for DHTML capable browser
if (document.getElementById || document.all || document.layers) {
	// test for NN/Gecko Layer API browser
	if(document.layers) {
	  isNav=true;				//set object string variables - use defaults
	} else {
	  if(document.all) {				//test for IE DOM browser, set object string variables
		isIE=true;
		coll="all.";
		styleObj=".style";
	  }	else {							// assume W3C DOM browser, set object string variables
		isDOM=true;
		coll="getElementById('";
		styleObj="').style";
		}
	}
}

var imgSize='640x480';

function show(imgobj) {	 if (imgSize != '160x120') { imgobj.visibility = "visible";}	}
function hide(imgobj) {	imgobj.visibility = "hidden";	}
function changeVisibility(Obj,overlayName) {


  var imgstr = "document." + coll + overlayName + styleObj;
  var imgobj = eval(imgstr);
  if ((Obj.checked == "1") || (Obj.checked == "true")) show(imgobj); else hide(imgobj);

}

function setVisibility() {
  var i;
  var objs= new Array("rivers","interstates","legend");
  var theObj

var values = new Array('OFF', 'OFF', 'ON');

  for(i=0;i<3;i++) {
	if (values[i] == "ON") {
	  theObj = eval("document.overlays.cb" + objs[i]);
      theObj.checked = true;
    } else {
	  theObj = eval("document.overlays.cb" + objs[i]);
	  theObj.checked = false;
	}
	changeVisibility(theObj,objs[i]);
  }
}
-->