def selected_polygons(polygon_gdf, **kwargs):
    """Creates a plotting instance of the boundaries of all selected polygons.

    Args:
        polygon_gdf (geo-dataframe): geo-dataframe containing the selected polygons.

    Kwargs:
        Geopandas-supported keyword arguments.

    Returns:
        ax: Matplotlib axis object.   
    """    

    ax = polygon_gdf.boundary.plot(**kwargs)

    return ax