Skewness (Sv) expresses the mean of the cube of deviation between all radial lengths and average radial length of an isovist (Benediky, 1979). In visibility graph terminology, it represents the point third moment for a location. When Skewness is positive, long radials are few in number and short radials many; when it is negative, the opposite is the case. Cave interiors have positive Skewness; space near columns, trees or outside corners have negative Skewness. The latter might correlate with a sense of exposure, the former with safety or power.
To determine Skewness, the Isovist_App calculates the difference between the current radial length and the average radial length. The resulting value is cubed, before being recorded as a mean over successive radial iterations for every point ‘V’ in plan. The final sum outcome is subsequently cube rooted, producing a relative value between 0 and infinity.
In notation form the calculation for Skewness is expressed as:
Where ‘Li’ is radial length, ‘Qv’ the average radial length from V; and ‘n’ the total number of radials sampled.