Average vertical velocity using PPMXL data as a function of Galactocentric Cartesian coordinates x, y (the position of the Sun is x = 8 kpc, y = 0) for | z | < 2 kpc. Only bins with error bars lower than 50 km s^-1 are plotted; black indicates larger errors or absence of data. The left panel is the weighted average of the bins without correcting for systematic errors of the proper motion. The right panel is the weighted average of the bins including the correction for systematic errors of the proper motion.