Kinematic features in the radial metallicity distribution as traced by open clusters. Top: distribution of open clusters in the V_ϕ–R diagram. The 332 open clusters with [M/H] estimation are shown as grey dots. The red area shows the kernel density estimate of that sample. The Galactic ridges identified by Ramos et al. (2018) are plotted as in Fig. 21. Middle: locally weighted scatterplot smoothing (LOWESS) regression of cluster V_ϕ as a function of R (solid line). The shaded area shows the 90% confidence interval of the LOWESS functions obtained by sampling within the uncertainties of the two variables. Bottom: Residuals between the cluster [M/H] values and the metallicities predicted by the radial metallicity gradient as in Table 3 as a function of R. As in the middle panel, the solid line shows the LOWESS function and the shaded area shows its 90% confidence interval.