I initially meant pyplot.xlabel and pyplot.ylabel (which I'm just used to seeing on all published graphs).

I assume your fatiando.vis.mpl preserves all of those and other features of matplotlib's functionality. I just wanted to be sure. A sentence stating that "the fatiando.vis.mpl contourf wrapper adds these custom features without interfering with matplotlib's functionality" would be as good as demonstrating it by adding basic things to your graph, like x&y labels.

That said, I understand extra labels would make the code snippet unnecessarily long, so it's up to you!