'Returns the patch used to draw the background of the axes.  It
is also used as the clipping path for any data elements on the
axes.
In the standard axes, this is a rectangle, but in other
projections it may not be.
.. note::
Intended to be overridden by new projection types.'

def _gen_axes_patch(self):

    import matplotlib.patches as mpatches
    grid_helper = self.get_grid_helper()
    t = grid_helper.get_boundary()
    return mpatches.Polygon(t)
