I think they belong together because one is really just a graphical representation of the other - and ``WCS`` has to be able to return a ``WCSAxes`` instance from the ``_as_mpl_axes`` method. In fact, users shouldn't even have to invoke ``WCSAxes`` directly, since they can do ``projection=WCS(...)``. But I'm interested to hear your opinion about why you feel they should belong in a different module?