map 是干什么用的？

[阿达King哥]

<map name="mainNav">
<area shape="rect" coords="523,8,634,31" href="#">
<area shape="rect" coords="387,8,498,31" href="#">
<area shape="rect" coords="249,8,360,31" href="#">
<area shape="rect" coords="7,7,87,31" href="#">
<area shape="rect" coords="113,8,224,31" href="#">
</map>

何解？