ABSTRACT
Geography treats mapped networks of cities with the concept of hierarchy. It is a tool to uncover reasons for the networks being what they are. A hierarchy, as dictionaries define it, is an arrangement of things in a graded series; and it has lots of intricacy. The map stresses various sizes and centralities for cities, which is a message about their grading in importance. Walter Christaller predicts a geometric progression in sizes of urban centres. August Loesch admits also other levels of hierarchy. This chapter introduces a train of reasoning for strengthening the Rank-Size model in its sovereignty. It considers two different types of reasoning. The first is a style with formal constructs of science, like that of hierarchy or other mathematical models used for statistical data analysis. The second type of reasoning consists of informal and explanatory arguments, because explanatory reasoning must interpret formal models, and derive conclusions from them or declare them invalid.
