Substructures in V_ϕ vs R plane revealed as a function of [Fe/H]. Top row: 2D density distribution showing the azimuthal velocity (V_ϕ) as a function of galactocentric radius (R) for the disc stars (i.e. Z_max <  1 kpc) to reveal the ridge-like features. The left panel shows all stars, the middle panel the metal-poor stars ([Fe/H]< −0.2), and the right panel the metal-rich stars ([Fe/H]>0.1). Bottom row: Same plots as above, which reveal undulations when coloured by the V_R. Both ridges and undulations are clearly seen for the full sample and the metal-rich stars, while these features are not as clear for the metal-poor stars. In the middle and right panels a dotted black line is drawn to represent the top sharp ridge seen in the top left density plot.