def expand_line(start_pt, stop_pt, line, expand_by=6):
    """ Creates buffer zone around a line.

    Parameters
    ----------
    start_pt : Shapely's Point object
    stop_pt : Shapely's Point object
    line : Shapely's LineString object
    expand_by : int
        This sets by how much you wish to expand the line.
        Defaults to 6.

    Returns
    -------
    zone : Shapely's Polygon object

    """
    line_expanded = line.buffer(expand_by)
    zone = start_pt.union(line_expanded).union(stop_pt)
    return zone