Extinction in the g-band over the survey region, derived from the maps of Schlegel et al. (1998). The extinction clearly varies considerably across this region of sky, but is not too extreme in the selected fields. The minimum and maximum values of ﹩E(B-V)﹩ within the CFHT fields (blue squares) are 0.04 mag and 0.22 mag, respectively, while the average and rms values are 0.07 mag and 0.03 mag, respectively.