Photometric offset estimated from the metallicity-dependent stellar locus. Top panels: initial offset with the homogenization from ISL, Δu_FeH. Bottom panels: final offset with the homogenization from ISL + ZS, . The left panels show the dependence on Galactic latitude b and the right panels on Galactic longitude l, showing pointings with positive and negative latitudes separately. In all the panels, the color scale shows the median metallicity in the pointing estimated from LAMOST spectra.