Frequency distributions of cloud areas for Ophiuchus and Perseus, derived using different threshold levels: A_G = 0.5 mag (left panels), 0.75 mag (centre panels), and 1 mag (right panels). The dashed vertical line indicates the median value. The red line shows the area from the POS perspective (i.e. the observed area) and the blue dotted line from the face-on perspective (perpendicular to the Galactic disk).