Fig. 14

depthmapX uses a geometric algorithm to analyse the visibility of each grid point in space. The red area shows high visibility (strong connection with other areas); the blue area shows low visibility. Generally, the redder the space, the higher is the probability various activities will occur there. It is evident that the P area has a significant connection with the red area. Moreover, the red area has obvious directionality, which indicates the possibility of an axis (Source: the authors)