To map the rectangle use the upper left and the lower right corners.
To map the circle use a point of the outer extremeties and the center.
To map a polygon use every point that changes a direction.
<map name="client">
<area shape="rect" coords="26,72,144,145" href="http://www.site1.com">
<area shape="circle" coords="262,112,42" href="http://www.site2.com">
<area shape="poly" coords="389,65,440,65,466,106,440,150,390,150,364,106" href="http://www.site3.com">
<area shape="rect" coords="2,2,503,214" href="http://www.site.com">
</map>