function layerswap(layername){
  if(document.getElementById(layername)){
    if (document.getElementById(layername).style.visibility=='visible'){
      document.getElementById(layername).style.visibility='hidden';
      document.getElementById(layername).style.display='none';
    }else{
      document.getElementById(layername).style.visibility='visible';
      document.getElementById(layername).style.display='block';
    }
  }
}