s, inv_trans)`` that define the
            transform and its inverse.  The callables should have signature::

                x_rect, y_rect = trans(x_curved, y_curved)
                x_curved, y_curved = inv_trans(x_rect, y_rect)

        extreme_finder

        grid_locator1, grid_locator2
            Grid locators for each axis.

        tick_formatter1, tick_formatter2
            Tick formatters for each axis.
        N)