SIMBAD references

We present new BVRI broadband photometry for the old open cluster NGC 188, based on an analysis of 299 CCD images either obtained by us, donated by colleagues, or retrieved from public archives. We compare our results on a star-by-star basis with data from 11 previous photometric data sets for the cluster. We homogenize and merge the data from all the photometric studies, and also merge membership probabilities from four previous proper-motion studies of the cluster field. Fiducial cluster sequences in the BV (Johnson) RI (Cousins) photometric system of Landolt ((ref???)1993, AJ, 104, 340) represent the principal result of this paper. These are compared to reference samples defined by (1) Landolt's standard stars, (2) the old open clusters M67 and NGC 6791, and (3) stars within 25 pc having modern photometry and precise Hipparcos parallaxes. In a companion paper, we show that our derived cluster results agree well with the predictions of modern stellar interior and evolution theory, given reasonable estimates of the cluster chemical abundances and foreground reddening. The individual and combined data sets for NGC 188 have been made available through our Web site.