버튼 클릭시 레이어 팝업 띄우기

<script type="text/javascript">
function showmap() {
 if(document.all.spot.style.visibility=="hidden") {
   document.all.spot.style.visibility="visible";
   return false;
 }
 if(document.all.spot.style.visibility=="visible") {
  document.all.spot.style.visibility="hidden";
  return false;
 }
}
</script>


<!-- a태그에 링크걸기 -->
<a href="#" onclick="showmap(spot);" title=""><img src="/경로/" alt="" /></a>


<!-- 레이어팝업 -->
<div id="spot" style="position:absolute; left:520px; top:500px; visibility:hidden;">
<img src="/경로/" alt="" />
</div>