Median V _R in the V _ϕ vs. R space for thin-disk stars. The red line corresponds to a ridge with a slope of −22 km s⁻¹ kpc⁻¹, while the slope of −8 km s⁻¹ kpc⁻¹ is shown in the green dashed line for a weak ridge and in the blue dashed line for a strong undulation. The turnover in the slope is found at R = 11.5 kpc.