This is what the zorder is used for. Artists should have
> a zorder attribute. The higher the zorder, the more in
> front an object is. I think they all default to 1.
Different types of "Artists" have different default zorders
In : from matplotlib.patches import Patch
In : from matplotlib.lines import Line2D
In : Line2D.zorder
In : Patch.zorder
So by default lines appear above patches....
See also examples/zorder_demo.py.