Friction of distance
The concept of friction of distance is based on the notion that distance usually requires some amount of effort, energy, time, and/or other resources to overcome. Because of this "friction", spatial interactions, especially transport and the particular case of human migration, will tend to take place more often over shorter distances; amount and intensity of interaction will decay with distance. Regardless of physical friction, the various costs are metaphorically assumed to correspond to forces that impede movements.
Friction, be it physical or metaphorical, may be a continuous, smooth function or may contain jumps; it may be constant, linear, or nonlinear or a combination of jumps and proportional effects, as with Intermodal freight transport and Intermodal passenger transport.
