Search

Greater Cairo (GC) is the seventh-largest metropolitan city globally. In recent decades, GC has witnessed massive urban expansion, which has yet to be empirically measured or characterized. This research seeks to explore the patterns of urban growth and changes in urban form in GC from 1973 to 2021 using remote sensing and geospatial metrics. Six Landsat images in 1973, 1984, 1992, 2003, 2013, and 2021 were used to explore urban growth in GC. Urban Land Density Function (ULDF), Landscape Expansion Index (LEI), and Fractal Dimension Index (FDI), were utilized to analyze various aspects of urban expansion. Additionally, the ratio of Land Consumption Rate (LCR) to Population Growth Rate (PGR) was calculated to assess the correlation between urban expansion and population changes. Our results reveal a substantial addition of 203 thousand hectares of urban areas over the last half-century. The ULDF highlights GC’s transformation from a condensed to a scattered urban landscape, particularly with the establishment of the New Administrative Capital in the vicinity. Edge expansion emerged as the principal type of urban growth throughout the research duration. The consistent increase in FDI from 1.44 in 1973 to 1.75 in 2021 signifies the fragmentation of the urban landscape. Moreover, the progressive rise in LCR from 0.023 in 1984 to 0.050 ​ha per person in 2021 suggests a steady expansion of low-density urban areas. Notably, the LCR-to-PGR ratio escalated from 0.878 in 1984 to 2.428 in 2021, indicating that urban expansion surpassed population growth. These results will help further understand the characteristics of GC’s urban expansion and may offer a scientific foundation for policymakers to reconsider the current horizontal expansion policy in GC.

The world is experiencing unprecedented urbanization, particularly through the continuous growth of megacities, leading to significant urban land expansion. The spatial layout and growth patterns of urban areas play a critical role in determining cities' sustainable development. However, the optimal path for cities undergoing rapid urbanization remains uncertain. This study examines four megacities—Tokyo, Seoul, Beijing, and Shanghai—and, from the perspective of urban land density, compares their patterns and processes of land expansion in 1990, 2000, 2010, and 2020. Findings reveal that the urban land area of China's megacities has expanded nearly fourfold over the past three decades. Meanwhile, Tokyo and Seoul have adopted a polycentric urban structure, becoming increasingly compact. In contrast, Beijing and Shanghai are only beginning to show signs of polycentric development. The study concludes that cities experiencing rapid growth should not impose excessive limitations on urban expansion. Polycentric and compact development has become a critical strategy for megacities. These insights offer valuable guidance for urban planning and sustainable development in both established and emerging megacities across East Asia.

The world is experiencing unprecedented urbanization, particularly through the continuous growth of megacities, leading to significant urban land expansion. The spatial layout and growth patterns of urban areas play a critical role in determining cities' sustainable development. However, the optimal path for cities undergoing rapid urbanization remains uncertain. This study examines four megacities—Tokyo, Seoul, Beijing, and Shanghai—and, from the perspective of urban land density, compares their patterns and processes of land expansion in 1990, 2000, 2010, and 2020. Findings reveal that the urban land area of China's megacities has expanded nearly fourfold over the past three decades. Meanwhile, Tokyo and Seoul have adopted a polycentric urban structure, becoming increasingly compact. In contrast, Beijing and Shanghai are only beginning to show signs of polycentric development. The study concludes that cities experiencing rapid growth should not impose excessive limitations on urban expansion. Polycentric and compact development has become a critical strategy for megacities. These insights offer valuable guidance for urban planning and sustainable development in both established and emerging megacities across East Asia. • We compared the spatial and temporal variation of urban land density in East Asian megacities over the past 30 years. • We divided urban area using contour lines of urbanness with different thresholds. • A multi-center development pattern may help alleviate urban development pressure. [ABSTRACT FROM AUTHOR]

Determining the optimal granularity, which has often been ignored in the analysis of urban expansion and its landscape pattern, is the core problem in landscape ecology research. Here, we calculate the optimal granularities for differently sized cities in the Huaihe River Basin of China based on scale transformation and area loss evaluation. Accordingly, we construct a landscape index and urban land density function to analyze urban expansion and landscape pattern. The results can be summarized as follows. (1) Within the first scale domain of the landscape indices, the optimal granularities of Zhengzhou, Xuzhou, Yancheng, Xinyang, and Bozhou are 60 m, 50 m, 40 m, 40 m, and 40 m, respectively, which are the optimal units in the study of urban expansion. (2) The urban land density decreases from the urban center to the outskirts, the urban core of each city is more compact than the outskirts, and the land density curve parameter α of Zhengzhou is the largest at 4.693 and its urban core the most compact. (3) There are significant spatial and temporal differences in the urban land densities of differently sized cities. The urban land density functions of different cities are similar before 2000; after that, they are similar to the standard inverse S-shaped function and the land use density curve of large cities is closer to the standard inverse S-shaped function than that of small- and medium-sized cities. (4) Large cities have faster expansion, much larger land density curve parameter c than medium- and small-cities, stronger linkage development with surrounding areas, and a higher degree of urban centralization. Urban expansion compactness was influenced by urban locations and functions except for urban sizes. This study offers a method for identifying the optimal granularities for differently sized cities and also provides information for the decision-making efforts that concern the rapid urbanization in major grain-producing areas of China. [ABSTRACT FROM AUTHOR]

The number and population of metropolitan areas have increased significantly during the last century, and in line with the increase in population, improved communications, global trends, and other significant factors, there have been many changes in the spatial development of these areas. These changes are observed in metropolitan areas of Iran during the same period, but there have been a few studies on the changes of these areas in Iran. In this study, the urban land density (U.L.D) function was used to investigate the spatial development trend in Shiraz metropolitan area from 1996-2016. The results show that the Shiraz metropolitan area has experienced a decentralized and scattered spatial form from 1996 to 2016. The pattern of changes in the region's spatial development during the years 1996-2006 and 2006-2016 shows that spatial development has become more decentralized and scattered. According to demographic analysis, the highest population density in 2006, 2011, and 2016 can be seen in the central buffer zone of Shiraz metropolis. Based on directional distribution (standard distance), the population distribution has moved to the northwest of the region. In addition, when analyzing the population distribution pattern, the Moran statistics shows that the region population is distributed in clusters. In general, the decentralized and dispersed spatial form and the formation of population clusters in the region's development process show an imbalance in the region's spatial and demographic development. Some of the significant effects of this phenomenon are urban fragmentation, social segregation, car dependency, and the destruction of agricultural lands and gardens. [ABSTRACT FROM AUTHOR]

Urban land density is an important factor to understand how cities expand. An “Inverse S-shape Rule” was implemented for the first time to analyze urban land density in Northeastern Thailand using the four cities Khon Kaen, Udon Thani, Nakhon Phanom, and Nong Khai as study sites. Land density function was tested using different data classification techniques from previous studies. Each city was investigated over two different time periods between 2002 and 2015. Declining pattern characteristics of metropolitan area density outward from city centers can be quantified by fitting the parameters to urban land density functions. An inverse S-shape function was identified as the best data fit. The four selected cities showed conventional density variation for decline in urban land area from city centers to outlying areas. Overall trend indicated that cities became more compact over time since the density differences between the urban core and urban fringe were greater with increasing infilling growth within the urban boundary. All four cities increased in size over time; however, the increasing amount of built-up land in the surrounding rural areas did not follow the same trend in each case. Some functional parameters required careful interpretation because of the linear shape of the city as in the case of Nakhon Phanom. Using highly detailed urban data resulted in lower densities of urban areas compared to the conventional pixel-based classification, and this affected the overall shape of the inverse S-shape function. The fitted parameters and their changing trends indicated that the urban land density function was useful for understanding urban form and urban sprawl in Thailand. Results can be used to develop a specific framework for other cities with similar attributes in the future.

Africa has been experiencing rapid urbanization, yet limited studies have systematically investigated urban growth dynamics across African cities. Using 25 cities as cases, we quantified urban growth and form changes in Africa via spatiotemporal analysis of urban land densities in concentric rings over three time points (1990, 2000, and 2014). The results show that African cities have rapidly grown both in population and built-up areas, which increased by about 4% and more than 5% per annum, respectively. Urban land density (defined as the proportion of the built-up area to the buildable area) in each concentric ring decreases from the city center to the urban periphery with diverse patterns among cities. Comparatively, small cities have a lower urban land density and a more dispersed urban form than medium-sized and large cities in Africa. The international comparisons between cities with over one million population in Africa, Asia (e.g., China and India), Europe, and North America (i.e., the United States) reveal that African cities have a relatively less compact urban form. Implications of these findings for the future of African cities are further proffered. • We analyze variations of urban land densities to quantify Africa's urban expansion. • Urban population and land grew by about 4% and over 5% annually from 1990 to 2014. • Small African cities have a lower urban land density and a more dispersed form. • African cities have a less compact form than cities in China, Europe, and India. [ABSTRACT FROM AUTHOR]

Abstract Rapid urbanization accelerates urban expansion, especially in populous areas, such as Southeast Asia. The urban forms and changes at the macro level and the dynamics at the patch level are interrelated. Considering its spatiotemporal interdependences and global-local interactions, we propose a framework to quantify urban expansion by combining macro patterns and micro dynamics. Taking three Southeast Asian megacities, Bangkok, Ho Chi Minh City (HCMC), and Manila, as examples, we calculate the urban land densities in concentric rings (macro pattern) and the proximity expansion index (PEI) of new urban patches (micro dynamic) to compare the urban form changes and expansion patterns based on Landsat imagery in 1990, 2000, and 2014. The results show that the urban form changes have close relationships with the local urban patch dynamics. The macro- and micro-level results in Bangkok and Ho Chi Minh City are interrelated and consistent and the explainable inconsistent results in Manila further reveal the necessity of combination of two scopes. The three megacities developed in different manners, thereby resulting in diverse urban forms and changes. Other methods and technologies combining macro and micro perspectives are encouraged to better understand urban expansion. Graphical abstract Unlabelled Image Highlights • Urban forms and changes are closely correlated with the dynamics of new urban patches. • Combining macro patterns and micro dynamics can fully understand urban expansion. • Three Southeast Asian megacities expand differently with diverse urban forms. [ABSTRACT FROM AUTHOR]

Urban land density is an important factor to understand how cities expand. An “Inverse S-shape Rule” was implemented for the first time to analyze urban land density in Northeastern Thailand using the four cities Khon Kaen, Udon Thani, Nakhon Phanom, and Nong Khai as study sites. Land density function was tested using different data classification techniques from previous studies. Each city was investigated over two different time periods between 2002 and 2015. Declining pattern characteristics of metropolitan area density outward from city centers can be quantified by fitting the parameters to urban land density functions. An inverse S-shape function was identified as the best data fit. The four selected cities showed conventional density variation for decline in urban land area from city centers to outlying areas. Overall trend indicated that cities became more compact over time since the density differences between the urban core and urban fringe were greater with increasing infilling growth within the urban boundary. All four cities increased in size over time; however, the increasing amount of built-up land in the surrounding rural areas did not follow the same trend in each case. Some functional parameters required careful interpretation because of the linear shape of the city as in the case of Nakhon Phanom. Using highly detailed urban data resulted in lower densities of urban areas compared to the conventional pixel-based classification, and this affected the overall shape of the inverse S-shape function. The fitted parameters and their changing trends indicated that the urban land density function was useful for understanding urban form and urban sprawl in Thailand. Results can be used to develop a specific framework for other cities with similar attributes in the future. [ABSTRACT FROM AUTHOR]

This work aims to model and relate the urban density and land surface temperature (LST) by a straightforward and efficient approach. Although the urban density-LST relation is widely addressed in literature, this study allows for its modeling and parameterization in an accurate way, providing a further scientific support for the city planning policy. The urban density and the LST analysis is carried out in the Bangkok area for the years 2004, 2008, 2012, and 2016; in this time interval, the city exhibited an evident urban expansion. Firstly, by using land cover maps obtained from Landsat reflective observations, the urban land density growth across the years studied is evaluated by applying a ring-based approach, a method employed in urban theory, providing urban density curves as a function of the distance from the city center. For each year, the urban density curve is well modeled by an inverse S-shape function, the parameters of which highlight an urban sprawl over the years studied and an outskirt growth in recent years. Then, employing 237 MODIS LST images, the night-time and daytime mean LST patterns for each year were processed applying the same ring-based analysis, obtaining LST trends versus distance. Albeit the mean LST decreases away from the city core, the daytime and night-time trends are different in both shape and values. The daytime LST exhibits a trend also modeled by an inverse S-shape function, whereas the night-time one is modeled by a quadratic function. Finally, the urban density-LST relationship is inferred across the years: For daytime, the relation is quadratic with a coefficient of determination r2 around 0.98–0.99, whereas for night-time the relation is linear with r2 of the order of 0.95–0.96. The proposed approach allows for reliable modeling and to straightforwardly infer a very accurate urban density-LST relationship.

Investigation and planning of future urbanization pathways necessitates knowledge and tools to better understand the physical spatial processes of urban expansion. In this study, the wave-shaped diffusion regularity of urban expansion in terms of the density of new urban land was detected and simulated with a Gaussian-based model, based on which the physical spatial process of urban expansion, as well as its long-term trends were characterized and understood. The Gaussian-based model provided a partitioning scheme to concentrically divide the urbanized areas of a given city into distinctive zones. Indices and methods were further developed to quantify compactness, rate, and development intensity of urban expansion processes. In particular, the model mathematically articulated how the macroscale urban form were invented from overlap of sequential physical spatial processes of urban expansion. The proposed model attained a fine fit with the density gradient of new urban land in 27 sample cities from 1990 to 2017, with an average R 2 value of approximately 0.87. The results revealed rapid urban expansion and path dependency in the compactness of urban expansion during this period. The concentric partitioning results in this study demonstrated tendency consistent with that reported in previous studies. The proposed model provides new insights into urban geography with a deeper understanding of the physical spatial processes associated with land urbanization • The physical spatial processes of urban expansion follow a wave-shaped regularity. • The regularity can be well represented by a Gaussian-based model. • The model provides a scheme for concentric partitioning of the urbanized areas. • Indices are developed for measurement of compactness and rate of urban expansion. • The model explains how the urbanized areas were created from sequential spatial processes of urban expansion. [ABSTRACT FROM AUTHOR]

Density analysis lies at the core of studies on urban expansion; however, many methods in urban land density analysis are arbitrary and suffer from the lack of an established foundation. We observed an “Inverse S-shape Rule” for urban land density that varies outward from an urban center by investigating 28 major cities in China at three time points. We proposed an inverse S-shaped function to formulate urban land density, which fit well for all of the cities in our sample using a nonlinear least squares fitting method. The parameters of the function explicitly describe the basic properties of an urban form. Based on the fitted functions, we derived an established method for the concentric partitioning of urban area and further proposed indicators to measure the urban compactness, urban expansion rate, and degree of urban sprawl. These indicators are practical for characterizing urban form and urban sprawl for either a single city or for multiple cities. A case study on major Chinese cities from 1990 to 2010 reveals that most of the cities expanded rapidly and became less compact and more dispersed during those two decades. However, most of the cities grew faster and showed more sprawl in the second decade compared to the first one. Discussions show that the model is also applicable for non-monocentric cities and possibly can be applied to many other geographical phenomena. [ABSTRACT FROM AUTHOR]

Indian cities face unplanned and rapid urbanization, yet limited studies investigate their urban growth dynamics systematically. Urban land density (ULD) analysis is crucial for developing countries worldwide, especially for populous countries like India. To understand the complexities of urban structure and its expansion, we propose a framework for quantifying urban densification by integrating its macro structure and micro dynamics. Five Indian cities are chosen as study areas based on economic categorization and city size. The macro-structure analysis is performed through a non-linear fitting of concentric density zones to derive an urban land density function (ULDF). The parameters of ULDF define the compactness and dispersion of urban expansion. The micro-urban form analysis is carried out by examining the spatial configuration of ULD. The study reveals that Tier-I city suffered from high compact urban growth. In contrast, Tier-II city with the elevated topography is found to have the highest urban land density at the city center in all studied years compared to the remaining chosen cities. The study also reveals that Tier-II city with plane topography has shown a significant increase in urban land density at boundaries. The rest of the chosen cities of Tier-III have contributed more toward dispersive growth. The spatial configuration of urban densities indicates that Tier-I and Tier-II cities have a close relationship in urban patches and class dynamics. Overall results from macro structure analysis depict that Tier-I and Tier-II cities are interrelated and consistent w.r.t. the ULDF, whereas, Tier-III city and town are explainable inconsistent. This inconsistency can be explained through a micro-urban form analysis. The study reveals the varied characteristics of developing cities, which would help policymakers and urban planners enhance the quality of urbanization and promote sustainable development. • We analyzed variation in urban land densities for different-sized Indian cities. • Our study interlinks the macro urban structure and micro urban form analysis. • The macro urban structure reveals the compactness and dispersion pattern of the cities. • The micro urban form analysis depicts urban land density's spatial configuration. • Large and mid-sized cities are found to be more compact than smaller cities. [ABSTRACT FROM AUTHOR]

Urban expansion across the globe accelerates land cover change and significantly influences the environment and human beings. Measuring the urban expansion process can help us better understand urban expansion dynamics and contribute to urban growth simulation and spatial planning. By using urban land density (defined as the proportion of the built-up area to the buildable area) as a spatial variable, we propose a new model to fit urban land density from the city center outwards (distance-decay rule), based on the assumption that urban shapes are formulated by the accumulation of micro-processes of urban growth. The model is based on simple math with only two parameters that clearly denote urban process characteristics. Using a sample set of 112 large cities around the world at three time points (1990, 2000, and 2014), the proposed model fitted urban expansion data very well, verifying its applicability. One parameter in the model that describes the density gradient can be used to measure the compactness of a city. The model can be easily extended to fit the intermediate process of a given time span and provide a clear indicator of the compactness of the process. The results of our case study clearly show disparities of global cities in terms of urban land compactness. For example, cities in Latin America and the Caribbean are the most compact, cities in Europe and East Asia are moderately compact, and cites in the United States, Canada, and Australia are the most sprawling. Furthermore, we identified a path dependence of urban expansion patterns as well as uneven compactness change trajectories in rapidly urbanizing areas. • Urban land density decays outwards from city center in an inverse S-shape. • We propose a process-oriented model to quantify the density distribution and urban expansion process. • The model provides a new tool to measure the urban form and urban expansion pattern. • The majority of cities showed stability in urban compactness from 1990 to 2014. • Temporal stability of urban form reflects the path dependence of urban expansion pattern. [ABSTRACT FROM AUTHOR]

Sustainable urban planning is essential in mediating the natural and built environments globally, yet, there is little progress as regards its attainment in developing countries. Rapid and unplanned urbanization continue to threaten the sustainability of many cities in Africa. By selecting Morogoro Municipal Council (MMC) in Tanzania as an example, this study applied well-known remote sensing techniques to understand the dynamics of urban growth and the implications for sustainable urban planning. The study analyzes spatio-temporal characteristics for eighteen years (2000–2018) based on urban land density using gradient and grid-based analysis to further examine land use and urban land density nexus. The results indicate declining urban land densities with distance to the city center, indicating a less compact and fragmented development at the urban fringes; and northward development with limited development to the south of MCC. The knowledge and understanding of the patterns of spatio-temporal conditions, land use planning, and management interventions in MMC are necessary for addressing the inadequacies associated with rapid urbanization within the study area. On this basis, we propose a shift from the modernist to the communicative planning strategy that strongly integrates the urban social, economic, and environmental imperatives, while being adaptable to evolving realities. This plan should also aim to curtail urban sprawl and create a viable city system and economically prosperous city structure for MMC. [ABSTRACT FROM AUTHOR]

This work aims to model and relate the urban density and land surface temperature (LST) by a straightforward and efficient approach. Although the urban density-LST relation is widely addressed in literature, this study allows for its modeling and parameterization in an accurate way, providing a further scientific support for the city planning policy. The urban density and the LST analysis is carried out in the Bangkok area for the years 2004, 2008, 2012, and 2016; in this time interval, the city exhibited an evident urban expansion. Firstly, by using land cover maps obtained from Landsat reflective observations, the urban land density growth across the years studied is evaluated by applying a ring-based approach, a method employed in urban theory, providing urban density curves as a function of the distance from the city center. For each year, the urban density curve is well modeled by an inverse S-shape function, the parameters of which highlight an urban sprawl over the years studied and an outskirt growth in recent years. Then, employing 237 MODIS LST images, the night-time and daytime mean LST patterns for each year were processed applying the same ring-based analysis, obtaining LST trends versus distance. Albeit the mean LST decreases away from the city core, the daytime and night-time trends are different in both shape and values. The daytime LST exhibits a trend also modeled by an inverse S-shape function, whereas the night-time one is modeled by a quadratic function. Finally, the urban density-LST relationship is inferred across the years: For daytime, the relation is quadratic with a coefficient of determination r2 around 0.98–0.99, whereas for night-time the relation is linear with r2 of the order of 0.95–0.96. The proposed approach allows for reliable modeling and to straightforwardly infer a very accurate urban density-LST relationship. [ABSTRACT FROM AUTHOR]