HTML and CSS Reference
The region defined by an <area> tag acts just like any other hyperlink:
when the user moves the mouse pointer over the region of the image,
the pointer icon changes, typically into a hand, and the browser may
display the URL of the related hyperlink in the status box at the bottom
of the browser window. [*] Regions of the client-side image map not
defined in at least one <area> tag are not mouse sensitive.