def build_slitw_format_dict(slitw_vals):
    """Build a dict mapping the slit width vals to matplotlib format statements"""
    idx = 0
    odict = {}
    slit_fmt_list = ['r.', 'g.', 'b.', 'k.']
    n_slit_fmt = len(slit_fmt_list)
    for slitw in slitw_vals:
        if slitw not in odict:
            odict[slitw] = slit_fmt_list[idx % n_slit_fmt]
            idx += 1
    return odict