Source: Adapted from Kansky (1963), p. 23.
Pi Index and the Shape of Transportation Networks
The Pi index is the ratio between the diameter (d; vertical axis) and length of the network (horizontal axis). A low Pi index is linked with a low level of network development (such as simple corridors) and a high value of Pi is linked with a more extensively developed network (a system of linked cities).
Pi Index
L(G) D(d) Pi
130 km 75 km 1.733
245 km 75 km 3.266