Metallicity difference between J-PLUS photometric values and APOGEE spectroscopic values, Δ[Fe/H], as a function of Galactic latitude b. Left panel: using 𝒳_ISL photometry. Right panel: using 𝒳_{ISL + ZSL} photometry. The solid lines in both panels show the best linear fitting to the data, with the gray areas depicting the 68% and 95% confidence intervals. The dashed lines mark zero difference. The dotted line in the right panel shows a difference of 0.02 dex.