Annis et al.               I    Model colors of BCG with z and
                                           look for E/S0 ridge-line
       AMF Kim et al. (2002)          I    Matched Filter algorithm looking for
                                           over-densities in luminosity & space
        CE Goto et al. (2002)         I    Color-cuts, then uses Sextractor
                                           to find and de-blend clusters
     F-O-F Berlind et al.             S    Friends-of-friends algorithm
    Groups Lee et al. (2003)          I    Mimics Hicksons Groups criteria
        BH Bahcall et al. (2003)      I    Merger of maxBCG & AMF
        C4 Nichol et al. (2001)     I & S  Simultaneous clustering of
                                           galaxies in color & space

  : Overview of past and present efforts to find clusters and groups of galaxies within the SDSS collaboration. In the data column, “I” is for SDSS imaging data and “S” is for SDSS spectral data.[]{data-label="cats"}

As first outlined in Nichol (2001), there are main four challenges to producing a robust optically–selected catalog of clusters. These are:

1.  [To eliminate projection effects. This problem has plagued previous catalogs of clusters and has been discussed by many authors (see, for example, Lucey et al. 1983; Sutherland 1988; Nichol et al. 1992; Postman et al. 1992; Miller 2000);]{}

2.  [A full understanding of the selection function. This has been traditionally ignored for optical 