Urbanization is not a uniform process thus the degree of urbanization varies from each urban centre (Zeng et al. 2016; Rahman et al. 2018). Urban development in developing countries like India are experiencing rapid urban explosion which need to be studied and monitored with modern techniques to quantify and impose sustainable practices to withstand the future urban challenges (Sudhira et al. 2003a, 2003b). Urbanization is now commonly regarded as one of the most important social processes, having enormous impact on the ecology at local, regional, and global scales (Turner 1990), controlled by the physical, social, and economic factors influencing the population growth, policies, and economic development (Saravanan et al. 2012; Bhagawat et al. 2017).
According to the United Nations – Department of Economic and Social Affairs (UNDESA 2021), 55% of the world’s population were reported from the urban areas during the year 2018. The report also estimated that urban areas are about to accommodate 66% of the total population by the year 2050; of which 90% of the urban growth will be reported from the Asian and African countries, especially China, India, and Nigeria.
For many years, demographic explosion and rural to urban migration has been the fundamental factors for rapid urbanization in the developing countries leading to radical land use conversion which causes problems like loss of natural habitat and biodiversity (He et al. 2014), poverty, over-population, employment, unhealthy housing conditions, inadequate infrastructure, hygiene and sanitation, poor water quality and pollution (UN-Habitat 2010; Nalini et al. 2017; Bhagat 2017). To a larger extent, urbanization is a good sign of development; however, there are meticulous sustainable urban plans based on quantitative urban analysis and implementation strategies are required to get the benefits of urbanization (Gisbert et al. 2017; Meijering 2018; Munier 2011).
Urbanization is an irreversible dynamic process at varying rate of expansion; the rate of expansion depends on the physical, social, economic, and infrastructure of the urban area (Li et al. 2003; Solon 2009; Aljoufie et al. 2011). Although, the physical conditions determine the establishment of the urban areas, to sustain the urban growth, three fundamental factors are necessitated viz 1. Function 2. Demography and 3. Economy (Batty 1994). In situations related to the decay of the urban centres or collapse of an urban centre, it could impart serious problems to the living and non-living systems. It is also noteworthy for the urban planners to enable urban centres continue functioning by satisfying 1) efficient production and delivery of the quality goods 2) resilient and flexible urban system in certain catastrophic events (Cabral et al. 2013; Preston et al. 2021; Brandão 2017).
In views pertaining to the existing urban conditions in many of the developing countries, implementation of the sustainable urban development plans have struck a bottle neck due to the manifold physical and functional complexities. A viable alternate approach would be “Differential Urbanization” to tackle the existing urban problems effectively while sustaining a balanced growth of the urban centre while it promotes the development activities on the surrounding towns where the plans can be implemented effectively, which alleviates pressure on the existing urban (Ourednicek 2007).
Hierarchical image classification is a promising technique applied in clustering similar image pixels based in spectral signatures (Lee and Crawford 2004; Tanguay et al. 2009). Multiple studies have shown increased efficiency in identifying and grouping the pixels based in hierarchical segmentation like road network extraction, wetland mapping and building extraction (Alshehhi and Prashanth 2017; Mao et al. 2020; Du et al. 2016). However, a general land use and land cover change analysis reveal the percent of change in the land use/cover, nevertheless, it may not reveal any pattern of the built-up spread or the characteristic of sprawl (Parvaiz et al. 2017; Kriti et al. 2018; Fan et al. 2018).
The need to quantify the growth of the city is firstly, to assess the improper and uncontrolled development of urban both within the city and on the outskirts. Secondly, to drive necessary planning and management policies for the sustainable growth, this requires analysis of spatial and temporal data to assess the trend over a period of time (Jegankumar et al. 2018; Mukesh et al. 2015), to understand the adaptive behaviour of the functional activities and local administrative planning for development ((Solon 2009; Nickayin et al. 2022).
There are plethora of metrics and statistical methods to quantify the urban sprawl; Bhatta et al. (2010) has compiled a number of measurements and techniques to quantify the urban sprawl and urban growth; modelling the urban sprawl quantifies the land area that are changed with respect to the temporal scale. Entropy model offers insightful results (Purvis et al. 2019) based on the entire urban into micro-regions of rings on the diversity of the urban sprawl (Sandipta et al. 2020; Juhi et al. 2019; Cho et al. 2021).
Urbanization can be studied in multiple dimensions with regard to the context considered. The urban form and morphology are one among the widely studied subjects. The varying urban growth is a complex phenomenon which can be better understood with the use of entropy method (Bitner et al. 2021), which is an appropriate technique for monitoring rapid urban sprawl and to quantify the related impacts on a quick temporal scale (Yeh 2001; Madhavi et al. 2016). In the recent past decades, studies on urban spatial growth have revealed multiple quantitative spatial characteristics like density, growth forms, shape, direction etc. (Dahal et al. 2016; Xu et al. 2007). Entropy and landscape metrics are indispensable techniques (Chen et al. 2018) in recent years to assess the spatial patterns, correlation, growth rate and trends, and the underlying impacts, which would provide insights to draw sustainable urban development plans (Ramachandra et al. 2012a, 2012b, 2013; Bharath et al. 2015, 2017).
Shannon Entropy method can be used to quantify the growth pattern (Mahesh et al. 2007). Urban sprawl has a close association with multitudinous urban related problems (Asfaw et al. 2018; Abdul et al. 2017). To effectively manage the problems, a sophisticated approach must be developed incorporating 1. Quantification of the sprawl 2. Location metrics of the sprawl and 3. Sprawl characteristics. Combining these factors to decompose the urban sprawl areas could reduce the complexities in studying them for sustainable urban management (Antoni 2002). Along with entropy methods Weighted Urban Proliferation (WUP) and Urban Permeation (UP) methods can be used in monitoring the urban development and various other spatial entities to associate in the decision making (Nazarnia et al. 2019).
For a sustainable urban transformation, governments must ensure the proper implementation of the Sustainable Developments Goals (SDGs) by the United Nations (Sudha et al. 2016). Sustainable urban development depends on the knowledge about the underlying problems and the driving factors. To quantify them, remotely sensed satellite imageries provide crucial data on spatiotemporal dynamics of the urban area (Aguilera et al. 2010). Certainly, these data play an important role in urban planning and resources management to make informed decisions (Phama et al. 2011; Jensen and Cowen 1999; Ahern 1991). Similarly, Fragile ecological regions demand sophisticated sustainable plans for its continued growth (Jayakumar et al. 2008; Fincher et al. 2014). Long term sustainable urban development goals must include 1) Continuous monitoring 2) Micro to regional level understanding and 3) Integration with socio-economic aspects (Artmann et al. 2019).