function showHideLayer(layerName)
{
   new_style = (document.getElementById(layerName).style.display == "none") ? "block" : "none";
   document.getElementById(layerName).style.display = 'block';
   document.getElementById(layerName).style.display = new_style;
}

function hideLayer(layerName)
{
   document.getElementById(layerName).style.display = 'none';
}

function showLayer(layerName)
{
   document.getElementById(layerName).style.display = 'block';
}