Over-density map of RC stars above (Z > 0) and below (Z < 0) the Galactic plane, in panels a and b, respectively. The bottom panels represent the distribution of the ratio of RC stars above and below the Galactic plane in the galactocentric coordinate system with ℓ range of 40° ≤ℓ≤320° and −10° ≤b ≤ 10° in panel c and |b| = 5° in panel d. The spiral-arm pattern (dot-dashed) follows the same colour codes as in Fig. 5.