this is back when every single byte mattered and saving a few MB was the difference between a good user experience and a bad one.
for those that never used this, you would do something like
<img src="funnycats.jpg" usemap="#funnycats-map">
<!-- the map defines clickable zones --> <map name="funnycats-map"> <shape="rect" coords="34,44,270,350" href="cats.html"> </map>
most ppl used something like Dreamweaver but bad-asses would do their own coordinates.