title: Calculate area of polygon given (x,y) coordinates
body: <p>I have a set of points and would like to know if there is a function (for the sake of convenience and probably speed) that can calculate the area enclosed by a set of points.</p>
  
  <p>for example:</p>
  
  <pre><code>x = np.arange(0,1,0.001)
  y = np.sqrt(1-x**2)
  
  points = zip(x,y)
  </code></pre>
  
  <p>given <code>points</code> the area should be approximately equal to <code>(pi-2)/4</code>. Maybe there is something from scipy, matplotlib, numpy, shapely, etc. to do this? I won't be encountering any negative values for either the x or y coordinates... and they will be polygons without any defined function.</p>
  
  <p>EDIT:</p>
  
  <p>points will most likely not be in any specified order (clockwise or counterclockwise) and may be quite complex as they are a set of utm coordinates from a shapefile under a set of boundaries</p>