Example of GMCs seen from different viewing angles of z-axis (face-on, left) and y-axis (edge-on, right). Note that y-axis ticks of the edge-on cases [panels (b) and (d)] are shown at the right-hand side. Only the cells with density >100 cm⁻³ are plotted; therefore, most of the coloured regions have been assigned to clouds. Panels (a) and (b) present the slice plots of face-on and edge-on views, respectively; panels (c) and (d) show projection plots of the same orientations. The representative region is located at the spiral arm with galactocentric radius of ∼6 kpc. It can be seen from panel (b) that clouds are flat in the z-axis, and consequently, the slice and projection plots of PPV|$\mathrm{_{face}^{H}}$| [panels (a) and (c)] show higher similarity and less crowding due to the small depth of the LOS, and vice versa for panels (b) and (d).