Shropshire Union: Telford's canals were much dearer to build but produced increased revenue by drastically reducing travel times. The law of refraction has been extended by Werner (1968) to allow the identification ofa transport route that minimizes total construction cost when an area is partitioned into a number of cost regions. The refraction analogue can be supplemented by network selection methods in which an optimum set of links may be chosen from a large range of possible connection patterns. models are discussed in location Developments in more advanced route Haggett and Chorley (1969. Chapter 4)