s-lines are defined as the lines obtained by extending both sides of all reflex angles as well as all walls terminating at a freestanding end point.

Sources Peponis, J., Wineman, J., Rashid, M., Hong Kim, S., Barna, S., (1997) On the description of shape and spatial configuration inside buildings: convex partitions and their local properties, Environment and Planning B, Vol 24, 761-781. pp.767-768.