City generics is a research choice to explore continuities of urban process across time and space. Central flow theory is interpreted as generic and is operationalized using the interlocking network model. A nuanced generic approach is developed that respects differences in inter-city relations found in dissimilar social worlds, defined as world-systems. This is illustrated through the application of the interlocking network model to extremely different world-systems – the contemporary world-economy and the ancient Mesopotamian world-empire. In both cases data is collected and analysed to reveal a city network at the centre of societal reproduction; advanced producer services are enabling of corporate globalization through cities; advanced divine services are enabling of spiritual-political change through cities. Both analyses produce credible geographical results so that similarities and differences in results can be discussed as generic inter-city relations.