In graph A, there are 5 links [(1,2), (2,1), (2,3), (4,3), (4,4)] and 3 connections [(1-2), (2-3), (3-4)]. On graph B, there is a path between 1 and 3, but on graph C there is no path between 1 and 3.
Connections and Paths
The Geography of Transport Systems
The spatial organization of transportation and mobility