I'm implementing draw.polygon from this example ( http://scikit-image.org/docs/dev/auto_examples/plot_shapes.html) I connected the dots to the verticies provided in poly and plotted over the imshow result: In [105]: plt.imshow(poly) In [107]: plt.plot(*zip(*poly), ls='--') In [108]: plt.scatter(*zip(*poly)) Which results in the attatched image. This is unexpected, no?