Attribute for <IMG ...>
USEMAP

USEMAP indicates that the image is an image map and uses the map definition named by this attribute. The name of the map is set by the NAME attribute of the <MAP ...> tag. Note that USEMAP requires that you precede the name of the map with a hash symbol (#). For example, the following code creates an image map named map1:

<DIV ALIGN=CENTER>

<MAP NAME="map1">
<AREA 
   HREF="contacts.html" ALT="Contacts" TITLE="Contacts" 
   SHAPE=RECT COORDS="6,116,97,184">
<AREA 
   HREF="products.html" ALT="Products" TITLE="Products" 
   SHAPE=CIRCLE COORDS="251,143,47">
<AREA 
   HREF="new.html" ALT="New!" TITLE="New!"     
   SHAPE=POLY COORDS="150,217, 190,257, 150,297,110,257">
</MAP>

<IMG SRC="testmap.gif" 
   ALT="map of GH site" BORDER=0 WIDTH=300 HEIGHT=300
   USEMAP="#map1"><BR>

[ <A HREF="contacts.html" ALT="Contacts">Contacts</A> ]
[ <A HREF="products.html" ALT="Products">Products</A> ]
[ <A HREF="new.html"      ALT="New!">New!</A> ]
</DIV>

which gives us this map:

Theoretically you can reference a map definition that is in an external file, but several browsers have problems with that contruct so it's best to stick to putting maps and map definitions in the same page.