Explain the naming of figure elements in a PyGMT figure

[seisman]

The figure below explains the anatomy of a matplotlib figure.

As you can see, the naming of figure elements is different between matplotlib and PyGMT.

1. tick labels in matplotlib are called annotations in PyGMT
2. axes in matplotlib is a region for plotting data. I don't think there is an equivalent in PyGMT
3. axis (e.g., x-axis and y-axis)in matplotlib is called axes in PyGMT, and is specified by WSENwsen.
4. spines in matplotlib are lines connecting the axis tick marks and noting the boundaries of the data area. In GMT/PyGMT, they're plotted by specifying l, r, t, or b.

These differences may confuse users coming from matplotlib. I think it would be good if we can create a similar figure and short tutorial, explaining the naming of figure elements in GMT/PyGMT.