When you have a polygon tag inside of an svg tag, beware of setting a vertex at 0,0 or up against the edge of the svg container in some similar manner.

Pain can arise with the stroke effect for your shape. It may end up looking skinny in places when being cut off by the bounds of the svg container. If the stoke is 2 pixels wide, well that entails 1 pixel of width both inside and outside of the polygon to make that effect and if 0,0 is a vertex then the 1px of the outer half of the stroke is going to disappear out of sight some at that point.