Even air-routes are, as Warntz(1961) has shown for the North Atlantic, confined to corridors; most movements flow along fixed channels-road pipelines, telephone wires. These features themselves pose distinct locational problems which are regarded here as part of a general class of network problems. Network location has a literature which includes some classic early studies (eg. Lalanne, 1863) but it is a top which has been strangely neglected in standard treatments of locational theory. It represents an area of common interest for both human geography represents an area theory and physicai geography (Haggett and Chorley, 1969) Here we develop some of the more elementary spatial models of network structure relating to location, density, and change over time. Readers are referred to Chapter 9 (see especially Section 9.7) for a description of measures of network structure.