A. Knowles (2002) is probably not alone in defining geography as ‘the study of spatial differentiation’. Within geography, spatial differentiation is seen as:

• • a process (see Krevs (2004) Dela 21 and Li and Wu (2006) Housing Studs 21, 5),

• • a causal mechanism (see Walker (1978) Rev. Radical Polit. Econs 10, 3),

• • a response (see Spark and Burt (2002) Soil Sci. Soc. Amer. J. 66).

The identification and measuring/mapping of spatial differentiation is fraught with difficulties. The European Union has proposed seven criteria for the differentiation of the European territory (Study Programme on European Spatial Planning—Final Report, 2001). There you will find the list of methods, together with the problems.