In an absolute context, distance in a network is a fixed attribute that does not change. For instance, the absolute distance between New York and Boston is about 310 km. The location of the nodes of such a network is also absolute and fixed. In a relative context, distance is a variable attribute that depends on numerous factors, such as the mode being used, its efficiency, regulations (e.g. speed limits) and congestion. Under such circumstances, some nodes of the network are “closer” when that are considered from a relative distance perspective instead of an absolute distance. So, while it took about 44 hours to travel between New York and Boston around 1800, by the end of the 20th century this figure was just above an hour using air travel (excluding time to go to and from airports).