Introduction

The rapid urbanization and expansion of cities are among the most prominent global trends of the current century (World Economic Forum 2015, 2016, 2017). In 1900, only 15% of the world’s population resided in urban areas. However, this figure rose to 56% in 2021, and projections indicate that it will reach 68% by 2050 (UN-Habitat 2022). Urbanization is an unavoidable global phenomenon where a significant number of individuals concentrate in urban regions, leading to the physical expansion of cities (Morshed et al. 2022).

Urbanization is often described as a transition process of the population from small isolated rural habitation, mainly an agrarian economy towards larger, much concentrated, and dense habitats dominated by industrial and service economies (National Research Council 2003). It is also linked with the sociological and physical phenomenon where the construction activity led by economic development accompanies rapid urban growth (Dewa et al. 2023). In the late 1800s and 1900s, Europe and North America experienced a swift process of urbanization, mainly driven by the industrial revolution and rapid economic development. However, in more recent times, Latin America, the Caribbean, and Eastern Asia regions have shown a less pronounced connection between urbanization, industrialization, and economic growth (United Nations 2015).

As more people migrate from rural to urban areas in search of better opportunities and improved living conditions, cities experience a surge in population growth, creating higher demands for housing, infrastructure, and services (Singh and Singh 2020; Berila and Isufi 2021). Inadequate urban planning and a lack of comprehensive land-use policies in response to this influx of people can lead to the uncontrolled expansion of urban areas into surrounding greenfield spaces, resulting in urban sprawl (Yang et al. 2020; Seevarethnam et al. 2021). Various studies globally have demonstrated that rapid urbanization has accelerated the pressure to accommodate the growing population, resulting in the outward pushing of city development (Monkkonen et al. 2018; Han et al. 2020; Berila and Isufi 2021). This has promoted low-density, car-dependent neighborhoods and the conversion of agricultural and natural land into urbanized zones (Hecht et al. 2020; Bonsu and Bonin 2023; Amare et al. 2023). Consequently, this pattern of urban growth is likely to foster urban sprawl, characterized by rapid and unplanned city expansion towards the outskirts (Daneshvar et al. 2019).

Rapid urbanization and urban sprawl are closely interconnected processes, with the former often acting as a catalyst for the latter. Urban sprawl refers to an unorganized and disorderly pattern of urban expansion, influenced by multiple factors, leading to inefficient utilization of resources (Rienow and Stenger 2014). This uncontrolled growth primarily results in a significant alteration of land cover, characterized by an increase in built-up and impermeable surfaces. Consequently, it becomes imperative to comprehend and evaluate the spatial and temporal aspects of urban growth in Indian cities to prevent unsustainable urbanization. To promote planned urban development, the United Nations adopted the Sustainable Development Goals (SDGs) in 2015, with goal number 11 specifically focusing on sustainable cities and communities (United Nations 2016). Goal number 11 highlights the importance of sustainable urban planning practices to mitigate the adverse impacts of urban sprawl. Given the anticipated rapid growth of urban areas in the upcoming decades, regular monitoring and assessment of urban expansion have become critically essential.

Urban sprawl studies conducted across the world have explored the unplanned and often uncontrolled expansion of urban areas into surrounding rural or undeveloped land (Ruiz et al. 2018; Al-Kofahi et al. 2018; Shao et al. 2020; Cieślak et al. 2020; Abdrabo et al. 2021). Researchers and policymakers have investigated the drivers, consequences, and potential solutions for urban sprawl in diverse regions (Fertner et al. 2016; Gao et al. 2016). In the USA, researchers have examined the emergence and impacts of sprawling suburban developments (Hamidi and Ewing 2014; Lee et al. 2018). Similarly, the studies focusing on European cities has analyzed urban sprawl patterns and their effects on cities and regions (Arribas-bel et al. 2011; Oueslati and Garrod 2015). China’s rapid urbanization has prompted studies focusing on land use change and the impact on the environment (Zeng et al. 2015; Feng and Wang 2019; Guan et al. 2020). India, Latin America, Australia, the Middle East, and Africa have also witnessed significant urban sprawl, leading to research on various aspects of this phenomenon, such as flooding. transportation systems, social inequality, and informal settlements (Rahnam et al. 2015; Rahman 2016; Devi et al. 2019; Silva and Vergara-Perucich 2021). These studies have collectively provided valuable insights into the challenges and complexities of urban sprawl, guiding the formulation of sustainable urban planning strategies worldwide. The primary objective of much of this published research is to detect, investigate, map, monitor, quantify, assess, and analyze urban sprawl in and around urban areas. With technological advancements, recent research endeavors have also aimed to model current and future patterns of urban sprawl.

To tackle the adverse impacts of urban sprawl on our environment and surroundings, it is crucial to undertake a thorough and critical examination of existing literature (Saini and Tiwari 2020). Such research endeavors contribute to the advancement of knowledge within the specific research field, shedding light on the latest developments and advancements. However, there is a scarcity of comprehensive research studies that aim to provide a holistic overview of the urban sprawl literature and synthesize the findings. Therefore, this study aims to critically review the existing body of research on urban sprawl to identify any gaps in knowledge. The outcomes of this study will assist researchers and authorities in gaining a comprehensive understanding of the urban sprawl phenomenon and making well-informed decisions.

Methodology

The methodology utilized in this study is depicted in Fig. 1. The approach involved the selection of peer-reviewed research papers and book chapters to examine the literature on urban sprawl and consolidate the findings as well as identify emerging trends.

Fig. 1
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Research flowchart

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Scopus database was the major source referred for this study. The keyword “urban sprawl” was used to search within “Article title, Abstract, Keywords”. A total of 6973 documents were found from the search. Thereafter, the “document type” selected were “article, book chapter, and review” which limited to 4451 documents only. The “language” selected was “English” and it limited to 3164 documents only. Furthermore, the “Subject area” selected were “Social Sciences,” “Environmental Science,” “Earth and Planetary Sciences,” “Engineering,” “Agricultural and Biological Sciences,” “Energy,” “Economics, Econometrics and Finance,” “Multidisciplinary,” “Arts and Humanities,” and “Computer Science,” which limited to 1500 articles only. Thereafter, these records from the Scopus database were exported with “Citation Information” and “Abstract & keywords” in CSV format. The relevant articles were selected through a content analysis carried out by meticulously reading the abstracts, adhering to the guidelines of the research. Specifically, the emphasis was on the alignment of each article with the focus on urban sprawl investigation. The content analysis enabled to organize the data in a reproducible manner. A critical assessment of each article was done to identify pertinent aspects related to the focus of this study. After excluding insignificant articles and duplicates, the final list comprised of 114 articles.

Thereafter, based on the 114 identified research papers, this study presents a detailed analysis of urban sprawl literature that focuses on definition, characteristics and consequences, domains, indicators/variables, methods/tools, and consequences. Lastly, the research gaps of urban sprawl studies identified through the literature review are presented.

Results

Definitions of Urban Sprawl

Urban sprawl is often considered a vague term since it has been interpreted differently by numerous researchers which is why it lacks a universal definition until date (Kovács et al. 2019). Galster et al. (2001) identifies that urban sprawl has been used by urban planners and researchers in various forms, which can be classified into six categories: (1) aesthetical perception through analysis of certain type of urban development, (2) causes of land cover conversion through built-up land cover change detection, (3) consequences of certain growth practices on the environment and society, (4) example to highlight the characteristics of sprawl, (5) patterns of urban growth through quantifying and measuring physical expansion of cities, and (6) process of urban development seen over a time period due to rapid urban expansion. Sudhira and Ramachandra (2007) assert that urban sprawl is the result of uncontrolled, uncoordinated, and unplanned growth, primarily observed on the outskirts of cities, along highways, and connecting roads between multiple cities and towns.

Furthermore, Bagheri and Tousi (2018) after an in-depth analysis of various definitions of urban sprawl, classify this phenomenon into four main categories: (1) spatial expansion system—characterized by chaotic and disorganized growth, sporadic diffusion, and distancing from the city center, (2) urban planning system—involving unplanned and uncontrolled growth, with development spreading beyond urban and functional boundaries, (3) land use and density system—encompassing changes in open spaces, agricultural lands, and rural areas, as well as single-use development and low-density construction, and (4) communication and accessibility system—associated with limited access to transportation modes and increased distances between work and home. Consequently, there is significant ambiguity in defining urban sprawl, and no universally accepted definition has been formulated thus far. However, a widely recognized understanding of urban sprawl describes it as the dominance of single land use, low-density built-up areas, scattered development, adverse environmental conditions, and unplanned expansion, ultimately leading to unsustainable land resource utilization.

Characteristics and Consequences of Urban Sprawl

Urban sprawl in developing countries like India is marked by distinct features, including the loss of agricultural land, deforestation, unregulated urban expansion, growth along major transportation routes, traffic congestion, and the degradation of water bodies and wetlands (Aithal et al. 2018; Kaur et al. 2019). The detrimental impact of urban sprawl extends not only to urban areas but also to the surrounding environment. Consequently, due to its extensive negative effects, urban sprawl has been classified as an unsustainable form of urban growth.

Urban sprawl is characterized by the predominance of low-density development, which drives the expansion of cities towards their outskirts (Weilenmann et al. 2017). This uncontrolled and unplanned growth pattern results in rapid changes in land cover, leading to unsustainable urbanization. Furthermore, the disperse growth observed in cities experiencing urban sprawl fosters leapfrog development, further exacerbating the problem. The conversion of agricultural land and the depletion of surface and sub-surface water resources due to built-up areas have caused significant land cover changes in and around human settlements. Inadequate land use planning and urban sprawl have increased reliance on automobiles, resulting in a rise in private vehicle ownership. Moreover, the peripheral areas of cities have experienced ribbon development along major roads, contributing to the spread of urban sprawl. The reduction of open spaces within and around cities has resulted in environmental degradation, the heat-island effect, and a decline in the overall quality of life. Overall, the significant characteristics of urban sprawl and their consequence are summarized and presented in Table 1.

Table 1 Characteristics and consequences of urban sprawl
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Driving Forces of Urban Sprawl

The driving forces are those factors which promotes urban sprawl. The driving forces of urban sprawl can be classified into major categories which includes, but are not limited to physical, social, economic, governance, and planning. These driving forces are further analyzed to gather their respective catalysts. The physical driving force of urban sprawl includes catalysts, such as lack of land availability at the core and geographical conditions. The social driving force includes catalysts, such as population growth, speculated growth, land ownership, higher cost of living and property in core, lack of affordable housing, single-family home, and country-living desire. The economic driving force includes catalysts, such as economic growth, industrial growth, purchase of land, and availability of banking services. The governance and planning driving force includes catalysts, such as inefficient governance, legal disputes, development charges, and improper planning policies. All the driving forces, catalysts and their description are exhibited in Table 2.

Table 2 Driving forces and catalysts of urban sprawl
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Measuring and Detecting Urban Sprawl

Urban sprawl is a dynamic phenomenon, and as a result, various methods have been developed to assess it. In general, the measurement methods for urban sprawl can be categorized into two groups: unidimensional and multidimensional approaches (Lopez 2014; Yue et al. 2016). Unidimensional methods are straightforward metrics that yield binary outcomes regarding the presence or absence of urban sprawl (Horn and Eeden 2018). On the other hand, multidimensional approaches concentrate on composite indexes that incorporate multiple interconnected dimensions (Arribas-bel et al. 2011). Researchers propose that composite indexes can capture the complexity of urban sprawl by incorporating detailed input data, thus offering a more nuanced understanding of the phenomenon (Paulsen 2014).

Scale of Study

The urban sprawl studies observed in the literature exhibited a lot of variation in the unit of investigation. This is majorly because the countries utilize various criteria related to administrative and political boundaries to classify an area as urban. These criteria may involve factors such as the inclusion of areas within municipal boundaries, blocks or counties, specific population thresholds (typically around 2000 individuals, although it can vary from 200 in Sweden to 50,000 in Japan), population density, economic activities (such as non-agricultural employment), or the presence of urban features like paved roads, electric lighting, and access to water supply, among others.

The researchers have examined urban sprawl from various perspectives, considering both administrative and spatial boundaries. The scale or unit of investigation predominantly used in urban sprawl studies is summarized in the below Fig. 2.

Fig. 2
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Scale of study

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Overall, it can be seen that 49 research papers were focused on individual cities or municipalities. These studies were limited to urban centers or administrative units. There were 25 research papers that were concentrated on districts or regions. There were 16 research papers that focused on metropolitan areas. There were only eight research papers that focused on a country or continent scale and covered issues that span across entire countries or entire continents. There were only six research papers that focused on urban agglomerations. These papers likely examine densely populated areas that include central cities and their neighboring towns or suburbs. There were 10 review papers which were not based on any specific city.

Indicators

The indicators of urban sprawl gathered from literature review are built-up growth, land-use mix, land cover change detection, density, socio-economic status, spatial geometry and landscape changes, transportation, and aesthetic measures. The major indicators of urban sprawl gathered from literature review are mentioned in Table 3.

Table 3 Indicators of urban sprawl
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Application of Remote Sensing and Geographic Information System

Remote sensing (RS) and geographic information system (GIS) have proven to be invaluable tools for researchers in monitoring and analyzing spatial challenges within society (Minakshi et al. 2017; Hecht et al. 2020). These technologies offer a cost-effective and efficient means of studying these issues by providing satellite imagery spanning different time periods, covering large areas, and enabling automation, which is often necessary for research purposes (Chrysoulakis et al. 2014). RS has been widely employed in studies on urban sprawl to extract built-up areas, determine growth rates, and detect changes in land cover over the years, e.g., Guangzhou, China (Yu and Ng 2007); Western Cape Province, South Africa (Horn and Eeden 2018); Europe (Arribas-bel et al. 2011); Teresina, Brazil (Espindola et al. 2017); Italy (Nol et al. 2014); and Vijayawada, India (Vani and Prasad 2020).

Application of Landscape Metrics

Landscape metrics, utilizing principles from information theory and fractal geometry, are extensively utilized to measure the structure and patterns of landscapes (Wang et al. 2018). Due to the complexity of land cover changes, a single metric is inadequate for monitoring, thus multiple correlated metrics are employed across space and time. To quantify the spatiotemporal dynamics in the fragmentation of built-up patches, the open-source software package FRAGSTATS v4.2.1 is utilized (Zhong et al. 2018). The computed landscape metrics through the FRAGSTATS v4.2.1 software is listed in Table 4.

Table 4 List of landscape metrics
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Application of Entropy Indexes

  1. A.

    Shannon’s entropy index—it is an indicator used to measure the intensity of urban sprawl (Chatterjee et al. 2016). It measures the degree of spatial dispersion or concentration of any geographical area. The value of entropy ranges from 0 to loge(n), where values closer to 0 indicate compact built-up areas and values closer to loge(n) specify dispersed built-up, i.e., urban sprawl. Rahman et al. (2011) examined Hyderabad-Secunderabad twin city during 1971 and 2005 and concluded an increase in the urban sprawl intensity over the years. Ramachandra et al. (2012) employed Shannon’s entropy index and detected the prevalence of urban sprawl in Greater Bangalore and the outskirts of the city. Mithun et al. (2016) used Shannon’s entropy index in the Kolkata Metropolitan Area to investigate urban sprawl.

  2. B.

    Relative entropy index—it measures the extent to which a variable is distributed among different categories or spatial zones, representing the maximum possible dispersion (Bagheri & Tousi 2018). The value of relative entropy falls between 1 and 0, with values closer to 1 indicating haphazard urban growth, i.e., urban sprawl, while values approaching 0 indicate balanced and even growth across all zones.

  3. C.

    Structure entropy index—it highlights the entire structural order formed by multiple categories of built-up areas (Jiang et al. 2016). The values of structure entropy are comparatively lower for the part of cities not developed to its potential while areas developed fully exhibits higher values.

Urban Sprawl Typologies

Three significant types of urban sprawl have been identified by Harvey and Clark (1965), namely continuous low-density development, ribbon development, and leap-frog development (Fig. 3). Low-density continuous development is the lowest order of sprawl typology and often opposes higher density development leading to poor land utilization. Ribbon development sprawl consists of developments within a few distances of either side of the major transportation corridors. It may be more expensive than low-density sprawl. Leap-frog development is the settlement pattern in patches which might be compact, but overall, it is a discontinuous development. It incurs considerable capital costs to provide urban services at the time of development.

Fig. 3
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Urban sprawl typologies as per Harvey and Clark (1965)

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Urban sprawl has been categorized into three categories by Wilson et al. (2003), namely infill development, edge-expansion, and outlying growth (Fig. 4). It is important to note that not all types of development are classified as sprawl; only edge-expansion and outlying urban growth are considered urban sprawl according to the researchers. This categorization method quantitatively assesses the development pattern of new built-up patches surrounding existing developments. The proximity or distance to the existing developed areas is a crucial factor in determining the typology of urban sprawl.

Fig. 4
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Urban sprawl typologies as per Wilson et al. (2003)

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Infill development refers to the construction of new built-up patches within existing vacant spaces of already developed areas. Edge expansion involves the creation of new built-up patches as an extension of existing developed areas, expanding along the edges. Scatter development refers to the independent formation of new built-up patches that do not overlap with existing developed areas. Similarly, landscape expansion index (LEI) based on the Wilson et al. (2003) is proposed by Liu et al. (2010).

The spatial urban sprawl typology categorizes the variations in urban growth based on adjacent neighborhood relationships (Fig. 5). It consists of five typologies: urban core, secondary urban core, urban fringe, ribbon development, and scatter development. These typologies provide a framework for understanding and classifying different patterns of urban sprawl in an area (Angel et al. 2007; Kantakumar and Neelamsetti 2015).

Fig. 5
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Urban sprawl typologies as per Angel et al. (2007) and Kantakumar and Neelamsetti (2015)

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Urban Sprawl Indexes

Feng et al. (2015b) and Jaeger and Schwick (2014) utilized knowledge of built-up area utilization, built-up growth rate, and spatial configuration to develop an urban sprawl index. Yue et al. (2016) used metrics like built-up density, discontinuity, and accessibility to create an urban sprawl index. However, many multivariable urban sprawl indexes require extensive multi-temporal data related to economy, environment, employment, and accessibility. Unfortunately, gathering such datasets is challenging in developing nations like India due to limitations in institutional capacity and weak inter-agency coordination (Jain and Korzhenevych 2019; Jain et al. 2019).

Research Gaps

The review of existing literature on urban sprawl studies reveals that there is no universally accepted definition of urban sprawl, and various studies use different measures and indicators to quantify it. This lack of standardized measurement makes it challenging to compare and generalize findings across different regions and cities. Furthermore, it was observed that limited number of comprehensive studies aim to holistically discuss the literature on urban sprawl and synthesize the findings and emerging trends. There is a need for more cross-city, cross-regional, and cross-country comparative studies to identify common patterns and unique challenges related to urban sprawl. There have been very few studies conducted on mid-sized cities with populations ranging from 0.5 to 5 million. Despite the increasing importance of mid-sized cities in achieving sustainable urban development, there is a lack of assessment of urban sprawl in these cities. Furthermore, with large cities reaching their carrying capacities, mid-sized cities are expected to experience higher levels of urban growth in the future, making the assessment of urban sprawl in these cities crucial.

While there have been studies on the drivers and causes of urban sprawl, a more comprehensive understanding is still needed. Factors such as population growth, transportation infrastructure, land-use policies, and economic dynamics play a role, but their interactions and relative importance require further investigation. Moreover, it is commonly believed that urban sprawl leads to negative environmental impacts, the specific relationships and mechanisms are not fully understood. More research is needed to assess the ecological consequences of urban sprawl on biodiversity, air quality, water resources, and overall ecosystem health. The social and economic implications of urban sprawl are not fully explored in the literature. The understanding of how the sprawl affects social equity, community dynamics, and economic development is crucial for designing sustainable urban policies. Urban sprawl may have implications for public health and well-being. For instance, increased reliance on cars and lack of walkability could lead to sedentary lifestyles and health issues. More research is needed to understand these connections.

It is also worth noting that there is limited research that considers urban agglomerations (UAs) as units of investigation for assessing urban sprawl. Considering UAs as the unit of analysis is appropriate because they encompass nearby areas where urban sprawl is likely to occur. Therefore, there is an urgent need for studies that assess urban sprawl in mid-sized cities and provide proper urban planning guidelines. Additionally, considering UAs as a unit of investigation can provide valuable insights into the occurrence and patterns of urban sprawl in the surrounding areas.

The urban sprawl indexes used in other studies require high computation methods and rigorous data. However, the use of such indexes in the developing or underdeveloped nations is not appropriate due to resource constraints and lack of data availability. Hence, an effective urban sprawl assessment method is required for the developing or underdeveloped nations to detect the intensity of urban sprawl and analyze its characteristics. Addressing all these research gaps would enhance our understanding of urban sprawl and help guide policymakers and urban planners in creating more sustainable and resilient cities.

Conclusion

This study provides a comprehensive analysis of the literature on urban sprawl to synthesize its different aspects and identify gaps in research. Urban sprawl is widely understood as the presence of single land use, low-density built-up areas, scattered development, and unplanned growth, leading to unsustainable use of land resources. The affected areas exhibit several key characteristics, including low-density development, rapid changes in land cover, dispersed growth, loss of agricultural land, depletion of surface and sub-surface water resources, dependence on automobiles, growth along major roads, and reduction in open spaces. These characteristics collectively contribute to the negative impacts associated with urban sprawl. As a consequence, urban development was observed towards the periphery, rise in unplanned urban growth, prevalence of leapfrog development, decline in non-built-up land cover, increase in private vehicle usage, prevalence of ribbon development, degraded environment, rise in heat-island effect, and poor quality of life.

The physical driving force of urban sprawl includes catalysts, such as lack of land availability at the core and geographical conditions. The social driving force includes catalysts, such as population growth, speculated growth, land ownership, higher cost of living and property in core, lack of affordable housing, single-family home, and country-living desire. The economic driving force includes catalysts, such as economic growth, industrial growth, purchase of land, and availability of banking services. The governance and planning driving force includes catalysts, such as inefficient governance, legal disputes, development charges, and improper planning policies.

The study examined various aspects related to the measurement and detection of urban sprawl, including the scale of analysis, indicators used, the application of remote sensing (RS) and geographic information system (GIS), landscape metrics, entropy indexes, and urban sprawl typologies. Previous studies have employed different scales to investigate urban sprawl, ranging from country/continent level to zone/ward/borough level. Indicators used for assessing urban sprawl encompass built-up growth, land-use mix, land cover change detection, density, socio-economic status, spatial geometry, landscape changes, transportation, and aesthetic measures. RS and GIS have been extensively utilized to detect and measure urban sprawl due to their capabilities in analyzing spatial data. Landscape metrics, including shape irregularity, fragmentation diversity, and the composition of built-up patches have been employed to identify the characteristics of urban sprawl. Entropy indexes, such as Shannon’s entropy index, relative entropy index, and structure entropy index have been used to detect urban sprawl. Overall, these approaches and methodologies have contributed to understanding and quantifying the phenomenon of urban sprawl. Multiple approaches were used to identify the typologies of urban sprawl, wherein Angel et al. (2007) and Kantakumar and Neelamsetti (2015) found to be predominantly used in studies.

There is a need for studies that comprehensively discuss the urban sprawl literature and synthesize the findings. The majority of urban sprawl studies have predominantly focused on large cities, neglecting the mid-sized cities, despite their increasing importance in accommodating urban growth. Furthermore, there is a lack of studies that consider urban agglomerations (UAs) as a unit of investigation for urban sprawl assessment, even though UAs are suitable for examining the occurrence of urban sprawl in nearby outgrowths.

Another research gap is the requirement for urban sprawl indices that utilize variables with data that can be gathered through open sources such as USGS, census reports, and socioeconomic surveys. Many existing indices rely on high computation methods and extensive data, which may pose challenges in developing nations with limited institutional capacity and weak inter-agency coordination. It is important to note that this study primarily focuses on the physical implications of urban sprawl, and there is a need for future research to consider social implications and examine urban policies and governance in the context of urban sprawl studies. Overall, addressing these research gaps will contribute to a more comprehensive understanding of urban sprawl and provide valuable insights for urban planning and policy-making.