Calculate the area of a polygon given as x(...),y(...)
    Implementation of Shoelace formula

def area(x,y):
    """
    Calculate the area of a polygon given as x(...),y(...)
    Implementation of Shoelace formula
    """
    # http://stackoverflow.com/questions/24467972/calculate-area-of-polygon-given-x-y-coordinates
    return 0.5 * np.abs(np.dot(x, np.roll(y, 1)) - np.dot(y, np.roll(x, 1)))