¹In a standard textbook on urban economics by Mills, Hamilton (1994), the authors raise the question: ‘What are urban areas?’. They argue that there are many urban concepts: town, city, urban area, metropolitan area, and the like. Some of these concepts are based on legal definitions, and hence these definitions vary across nations. Others are based on population figures and reflect the fact that in urban areas the average population density is higher than elsewhere. The authors provide the following basic description: ‘Thus the fundamental and generic definition of an urban area, or metropolitan area, is a place with a much higher population density than elsewhere’ (p. 3). It is thus apparent that the concept ‘urban’ is not a clearly operational term. In our study, we use this term as a general description of a place or area with a relatively high concentration of people in a demarcated built environment. To be slightly more precise, in the present study, we adopt the following nomenclature in the present paper (see the Dictionary of Human Geography, edited by Gregory et al. (2009)):

• urbanization: has often been understood as a process of human distancing from first nature. In cities, nature became a residual or artificial category limited to parks, zoos and urban – mostly ornamental – gardens.
• city: today, a more generic usage of this term refers to an urban demographic, economic and above all political and jurisdictional unit, usually bigger than a town.
• agglomeration: the association of productive activities in close proximity to one another. It typically gives rise to external economies associated with the collective use of the infrastructure of transportation, communication facilities and other services. Agglomeration also facilitates the rapid circulation of capital, commodities and labour.
• urban areas: may be cities or towns and are characterized by a higher population density in comparison with the areas surrounding them.