Aframework for measuring the formation of extended metropolitan regions, case study: the large metropolitan region of Tehran, Alborz, and Qazvin

The rise of urbanisation has led to shifts in the literature and terminology employed by urban and regional planning experts. Prior to the 20th century, scientists primarily utilised micro-scale concepts such as urban, rural, and occasionally metropolitan to elucidate residential patterns. However, during the 20th century, the growing process of urbanisation resulted in the emergence of various spatial and residential development patterns. The expansion and progress of extended metropolitan regions is a growing phenomena. Research on extended metropolitan regions is a highly complex research area in regional planning due to the lack of established criteria to determine their formation. The absence of fixed indicators to recognise extended metropolitan regions as a distinct planning scale has contributed to the complexity and unfamiliarity of this phenomenon. Furthermore, the formation can yield both favourable and unfavourable outcomes across various dimensions. For instance, in the economic realm, it can lead to increased access to labours and job creation, as well as increased access to land and affordable housing. However, it can also result in an increase in the poverty rate. In the social sphere, it has the potential to enhance the quality of life in particular area, but it may also lead to a decline in overall quality of life. From an environmental standpoint, it can serve as a platform for addressing regional environmental issues, but it may also contribute to the bring green and open spaces under development. In terms of physical-spatial dynamics, it can promote decentralisation, but it can also lead to centralization. Lastly, in the managerial-institutional domain, it can foster cooperation in addressing common challenges, but it can also exacerbate fragmentation and dispersion of institutions. Neglecting these aspects may result in the negative consequences outweighing the positive ones. This research aims to establish a comprehensive framework for assessing the formation of extended metropolitan regions. The framework has been applied to analyse the urban-region of Tehran, Alborz, and Qazvin. Observing nocturnal light maps prompts the notion that the Tehran-Alborz-Qazvin boundary is becoming an expanded metropolitan area. To achieve the stated objective in this study, an analysis of the theoretical principles concerning extended metropolitan regions, spatial planning, and spatial structure and organisation was conducted. As a result, a set of indicators for measuring the development of extended metropolitan regions was proposed. These indicators were categorised into three groups: morphological, functional, and auxiliary indicators. Subsequently, a proposed analytical framework has been devised to identify the establishment or absence of the extended metropolitan region and to ascertain its level of advancement and progress. The proposed framework incorporates a scoring system that utilises both morphological and functional examination of spatial organisation. Through the analysis of the given indicators using GIS and Excel software, the study determined that the metropolitan region of Tehran, Alborz, and Qazvin is now in its early stages of development. Indeed, the focal point of the expanded metropolitan area remains in Tehran and Alborz province. However, the assessments also verify the migration of the expanded metropolitan area towards Qazvin