<p>Note that in the case of a concave polygon the center of the bounding rectangle might be completely outside the polygon. If your polygons might be concaved, I'd recommend using the center of the biggest inscribed circle as the "center" of the polygon. You can see a simple enough algorithm <a href="http://arxiv.org/ftp/arxiv/papers/1212/1212.3193.pdf" rel="nofollow">here (p. 4)</a>. If your task is to place a label on the polygon, this will also give the most aesthetically pleasing results (in which case I'd recommend using this method even if your polygons might not be concave).</p>
How to get the center of a polygon in google maps v3?
<p>It doesn't need to be 100% correct, it can be the center of the bounding rectangle.</p>