What does a 4-element tuple argument for ‘bbox_to_anchor’ mean in matplotlib?

In the “Legend location” section of the “Legend guide” in the matplotlib website, there’s a small script where line 9 is plt.legend(bbox_to_anchor=(0., 1.02, 1., .102), loc=3, ncol=2, mode="expand", borderaxespad=0.). All the tuples I’ve seen passed to bbox_to_anchor have 2 elements in it, but this one has 4. What does each element mean if the tuple passed has 4 elements?

Setting aspect ratio of 3D plot

I am trying to plot a 3D image of the seafloor from the data of a sonar run over a 500m by 40m portion of the seafloor. I am using matplotlib/mplot3d with Axes3D and I want to be able to change the aspect ratio of the axes so that the x & y axis are to scale. An example script with generated data rather than the real data is: