We present complexity of the Galactic outer disc by fitting the stellar volume densities of the red giant branch stars with a two-disc component model. The discs are confirmed to extend to R ∼ 19 kpc. The radial density profile of the discs shows two breaks at R ∼ 11 and ∼ 14 kpc, respectively, which separate the radial profile into three segments with different scale lengths of 2.12 ± 0.26, 1.18 ± 0.08, and 2.72 kpc at R < 11, 11 ≤ R ≤ 14, and R > 14 kpc, respectively. The first break is likely due to the sudden drop in the radial profile of the thin disc, which may be an evidence of the radial migration. Beyond 14 kpc, the thick disc becomes prominent and the transition from thin to thick disc leads to the second break. This implies that the geometrically defined thick disc is more radially extended than the thin disc. This is also supported by the larger scale length of the thick disc than that of the thin disc. Meanwhile, the scale height of the thicker component increases from 0.637 +0.056 −0.036 at R = 8 to 1.284 +0.086 −0.079 kpc at R = 19 kpc, showing an intensive flared disc. Moreover, rich substructures are displayed in the residuals of the stellar density. Among them, the substructures D14 + 2.0 and O14 − 1.5 show a north-south asymmetry, which can be essentially explained by southward shifting of the thick disc. However, no significant overdensity is found for the Monoceros ring. Finally, the thick disc shows a ripple-like feature with unclear origin at 9 < R < 10.5 kpc.

We present a three dimensional velocity analysis of Milky Way disk kinematics using LAMOST K giant stars and the GPS1 proper motion catalogue. We find that Galactic disk stars near the anticenter direction (in the range of Galactocentric distance between R = 8 and 13 kpc and vertical position between Z = −2 and 2 kpc) exhibit asymmetrical motions in the Galactocentric radial, azimuthal, and vertical components. Radial motions are not zero, thus departing from circularity in the orbits; they increase outwards within R 12 kpc, show some oscillation in the northern (0 < Z < 2 kpc) stars, and have north-south asymmetry in the region corresponding to a well-known nearby northern structure in the velocity field. There is a clear vertical gradient in azimuthal velocity, and also an asymmetry that shifts from a larger azimuthal velocity above the plane near the solar radius to faster rotation below the plane at radii of 11-12 kpc. Stars both above and below the plane at R 9 kpc exhibit net upward vertical motions. We discuss some possible mechanisms that might create the asymmetrical motions, such as external perturbations due to dwarf galaxy minor mergers or dark matter sub-halos, warp dynamics, internal processes due to spiral arms or the Galactic bar, and (most likely) a combination of some or all of these components.