def projected_area_factor(ax, original_crs):
    """
    Helper function to get the area scale of the current projection in
    reference to the default projection.
    """
    if not hasattr(ax, 'projection'):
        return 1
    if isinstance(ax.projection, ccrs.PlateCarree):
        return 1
    x1, x2, y1, y2 = ax.get_extent()
    pbounds = \
        get_projection_from_crs(original_crs).transform_points(ax.projection,
                    np.array([x1, x2]), np.array([y1, y2]))

    return np.sqrt(abs((x2 - x1) * (y2 - y1))
                   /abs((pbounds[0] - pbounds[1])[:2].prod()))
Helper function to get the area scale of the current projection in
    reference to the default projection.