Various methods have been used to devise a hierarchy of towns, including comparing the number and type of functions, using multivariate analysis, measuring the interaction between a settlement and its field, ranking settlements by the size of their spheres of influence; and using graph theory. Recent rankings have been based on quality of life (Rogerson in F. T. Seik et al., eds (2000); Berger et al. (1987) Soc. Sci. Quart. 68) or on urban competitiveness (Rodinelli and Vastag (1997) Econ. Dev. Qly. 11). The 2007 China Urban Competitiveness Study (Hong Kong) found, unsurprisingly, that Hong Kong was at the top of the Chinese hierarchy. A. Christopher (2012) has an investigation of the rank-size rule in Delta state, Nigeria.