Both topics, planning cultures and shrinking cities can be labelled emerging topics in spatial planning. Just like planning cultures, shrinking cities has been widely underrepresented in international comparative urban and regional research. The shrinking city phenomenon is a multidimensional process, comprising cities, parts of cities or metropolitan areas that have experienced dramatic decline in their economic and social bases. In consequence, shrinking cities and planning systems are influenced by various factors resulting in on-going changes over time. In particular, globalisation and Europeanization processes have brought major changes to the development of cities, of institutional structures, and of processes of planning.

In order to adequately analyse planning culture in the context of shrinking cities, the definition should be flexible, considering several aspects. First of all it should be noted that both cities and planning are not static but in a constant flux. Moreover, culture is not a fixed and independent variable, as it is not only influenced by endogenous aspects, but also shaped by exogenous factors. Therefore Planning culture deals with formal and informal processes and practices of how spatial planning is formally and informally institutionalized, performed and conceived. It refers to the interpretation of planning tasks, the ways of recognizing and addressing problems, the handling and use of certain rules, procedures and instruments, or ways and methods of public participation.

So far it has proven difficult to define shrinking cities because shrinkage is such a multi-causal and multi-faceted phenomenon. Although there is no clear-cut definition of shrinking cities, contemporary research work on this topic has referred to population loss as the main indicator of urban shrinkage.
To specify the significance of population losses the city must have lost a certain percetage of people per year or a certain total share of inhabitants, in each case over a certain period of time.