Gang Xu

Wuhan University | WHU · School of Resources and Environmental Science

It is widely observed urban land expands faster than population grows, which results in declining urban population densities over time. However, it is not known how densities decline. By taking 35 major Chinese cities as examples, we propose an exponential model to quantify the temporal decline in urban population densities from 2001 to 2015. The a...

Urban scaling law quantifies the disproportional growth of urban indicators with urban population size, which is one of the simple rules behind the complex urban system. Infectious diseases are closely related to social interactions that intensify in large cities, resulting in a faster speed of transmission in large cities. However, how this scalin...

Allometric urban scaling law quantifies disproportional relationships between urban indicators and city size, which has been reported across developed countries and parts of the global south, but its applicability in Africa is neglected. Here, taking built-up areas derived from remote sensing in more than 7000 African agglomerations in 2015 as exam...

The spatial agglomeration of urban elements results in the center-periphery urban structure, but the difference in spatial gradients of socioeconomic and physical elements is unclear. This study investigates how urban land density (ULD) and nighttime light intensity (NLI) decline with the distance to center(s) using the inverse-S function. Taking 3...

Spatial inequality erodes social cohesion and political stability, impacting global sustainable development and human well-being. This study examines spatial inequality in China across economic, social, environmental, infrastructural, and innovation dimensions, exploring how these inequalities evolve with economic development. Drawing on the Sustai...

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 rem...

Urban expansion models (UEMs) help unfold the mechanism, future pathways, and relevant repercussions of urban landscape dynamics. Although, a plethora of UEMs have been developed, the field of open-access modeling platform for urban expansion simulation still presents gaps in terms of representing urban development events, regulating multilevel urb...

Urban expansion often occurs at the expense of cropland loss, posing challenges to sustainable urban growth and food security. However, detailed investigations into urban expansion and cropland loss remain limited, particularly in regions with varying levels of urbanization. Here, we take Guangdong Province, China, as a case study to exemplify how...

Infectious diseases depend on intensified social intercourse within large cities, resulting in a super-linear allometric scaling law with city size. But how this scaling relationship changes throughout an evolving pandemic is seldom studied and remains unclear. Here, we investigate allometric scaling laws between cases/deaths and city size and thei...

The supply and demand of ecosystem services (ES) present apparent spatial heterogeneities within cities, with a higher demand but limited supply in urban centers, and vice versa in suburban and rural areas. However, there is still a lack of theory and relevant quantitative tools to quantify the distribution patterns and spatial mismatches of ES sup...

The urban form influences the quality of urban functions and is strongly correlated with the sustaining capabilities of urban development. However, in the context of rapid urbanization, unreasonable land expansion as a universal phenomenon poses a great challenge for urban management. Notably, the urban expansion process is self-organizing, and the...

The net primary productivity (NPP) of vegetation is an important indicator reflecting the vegetation dynamics and carbon sequestration capacity in a region. In recent years, China has implemented policies to carry out ecological protection. To understand the changes in the distribution of vegetation NPP in China and the influence of climate factors...

After successfully inhibiting the first wave of COVID-19 transmission through a city lockdown, Wuhan implemented a series of policies to gradually lift restrictions and restore daily activities. Existing studies mainly focus on the intercity recovery under a macroscopic view. How does the intracity mobility return to normal? Is the recovery process...

Most intensive human activities occur in lowlands. However, sporadic reports indicate that human activities are expanding in some Asian highlands. Here we investigate the expansions of human activities in highlands and their effects over Asia from 2000 to 2020 by combining earth observation data and socioeconomic data. We find that ∼23% of human ac...

Identifying the driving factors of urban development and revealing its growth path is an important step toward better understanding the dynamic process of urban evolution. We proposed a theoretical framework of the mechanism of urban development, taking wealth production as an example from the aspects of local, network and systemic dependence to ch...

The application ofGIS technologies has extended from natural sciences to social sciences. The emerging spatial–temporal big data supported by GIS has broad applications in social governance. Through a unified time–space reference, multisource big data from different departments can be linked and organized, forming a block data.Acloud platform based...

China's rapid urbanization is not only the expansion of urban land, but also the three-dimensional expansion of buildings, which are physical expansion of the city. However, whether urban social and economic activities and urban vitality match the physical expansion of cities is still unclear. Taking Shanghai as an example, we acquired the high-res...

China's rapid urbanization has resulted in a dramatic loss in cultivated land that threatens future food security. Local and central government have successively launched a series of Low-slope Hilly Regions Comprehensive Development and Utilization (LHRCDU) pilot projects (i.e., the rudiment of China's hillside urbanization) since 2006 to balance t...

Objectives: Geospatial data and computing plays an important role in the era of big data and artificial intelligence(AI), and provides a dimension of social studies in term of ontological, methodological, and epistemologs aspects. Methods: This interview invited some influential scholars from the fields of sociology, geo⁃informatics, computing scie...

Urban boundary is the spatial basis for urban statistics and urban planning. However, the city definition by which the urban boundary is determined is not comparable among different countries. A globally consistent delimitation of hierarchical urban boundaries (HUBs) is rare but urgently needed. In this research, we proposed a model to consistently...

Quantifying the aggregation patterns of urban population, economic activities, and land use are essential for understanding compact development, but little is known about the difference among the distribution characteristics and how the built environment influences urban aggregation. In this study, five elements are collected in Wuhan, China, namel...

As an infrastructure-related urban indicator, urban land theoretically has a sub-linear scaling relationship with urban population, which has been evidenced around various urban systems. However, scaling relationships between different types of urban land such as residential, industrial land and population size are still unclear, which helps to und...

The lack of detailed COVID-19 cases at a fine spatial resolution restricts the investigation of spatial disparities of its attack rate. Here, we collected nearly one thousand self-reported cases from a social media platform during the early stage of COVID-19 epidemic in Wuhan, China. We use kernel density estimation (KDE) to explore spatial dispari...

The COVID-19 epidemic widely spread across China from Wuhan, Hubei Province, because of huge migration before 2020 Chinese New Year. Previous studies demonstrated that population outflows from Wuhan determined COVID-19 cases in other cities but neglected spatial heterogeneities of their relationships. Here, we use Geographically Weighted Regression...

Urban scaling laws assume that the performance of a city largely relies on its urban population size. However, two cities with the same population size may have vastly different economic outputs, which reveals that factors apart from urban size (a measurement of intra-urban interactions) determine their economic outputs. Economic production is esse...

Understanding the scaling characteristics in China is critical for perceiving the development process of rapidly urbanising countries. This paper conducts a comprehensive scaling analysis with quantitative assessment of a large number of diverse urban indicators of 275 Chinese cities. Our findings confirm that urban scaling laws can also be applied...

The lockdown of cities against the COVID-19 epidemic directly decreases urban socioeconomic activities. Remotely sensed night-time light (NTL) provides a macro perspective to capture these variations. Here, taking 20 global megacities as examples, we adopted the NASA’s Black Marble NTL data with a daily resolution to investigate their spatio-tempor...

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...

The urban heat island (UHI) effect in cities and its driving factors have long been investigated. 3D buildings are key components of urban structures and have notable effect on UHI effect. However, due to the incomplete 3D building information in urban database, only a few studies investigated the impact of 3D building morphology factors on the lan...

Spatio-temporal characterization of urban expansion is the first step towards understanding how cities grow in space. We summarize two approaches used in urban expansion measurement, namely, concentric-ring analysis and grid-based analysis. Concentric-ring analysis divides urban areas into a series of rings, which is used to quantify the distance d...

Deep learning provides a promising approach for air pollution prediction. The existing deep learning-based predicted models generally consider either the temporal correlations of air quality monitoring stations or the nonlinear relationship between the PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) concentrations and ex...

Cities are centers for the integration of capital and incubators of inventions. Attracting venture capital (VC) is of great importance for cities to advance in innovative technology and business models towards a sustainable and prosperous future. Yet we still lack a quantitative understanding of the relationship between urban characteristics and VC...

A quantitative description is the basis for correctly understanding the urban expansion process. Previous approaches were dedicated to identifying expansion types based on the boundary sharing rate, thereby depicting the evolution of urban expansion. These methods, however, focused on describing neighborhood relations and ignored urban global expan...

As one of the 17 Sustainable Development Goals, it is sensible to analysis historical urban land use characteristics and project the potentials of urban sustainable development for a smart city. The cellular automaton (CA) model is the widely applied in simulating urban growth, but the optimum parameters of variables driving urban growth in the mod...

Cities are centers for the integration of capital and incubators of invention, and attracting venture capital (VC) is of great importance for cities to advance in innovative technology and business models towards a sustainable and prosperous future. Yet we still lack a quantitative understanding of the relationship between urban characteristics and...

This study questions the frequent overemphasis on population growth aspects of African urbanization with little consideration of the spatial extent by analyzing the influence of population growth on the spatial expansion of the Morogoro urban municipality (MUM) in Tanzania between 2000 and 2016. Shannon's Entropy, a random forest supervised classif...

In the context of urbanization and sustainable development, efficient urban land use is essential, especially in China, the world's most populous country. Within this context, the law of urban scaling reveals the nonlinear scale relationship between urban indicators and urban population, which can be applied to adjust the bias of the raw or the per...

Rapid urbanization and land expansion persistently shrink urban green field, which accelerates soil sealing and land degradation. Spatio-tempral pattern analysis of green field caused by soil sealing contributes to its protection but quantitative tools are rare. Taking Shanghai-Hangzhou Bay Urban Agglomeration (SHBUA) as an example, we interpreted...

The emergence of social media provides a rich source of posts to facilitate situational awareness and management during crisis events. Since interactions within social media users are frequently used to establish social networks, previous studies have explored how social media contributes to the information diffusion about crisis events. However, m...

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,...

Numerous urban indicators scale with population in a power law across cities, but whether the cross-sectional scaling law is applicable to the temporal growth of individual cities is unclear. Here we first find two paradoxical scaling relationships that urban land sub-linearly scales with population across cities, but urban land expands faster than...

Methods for estimating the spatial distribution of PM2.5 concentrations have been developed but have not yet been able to effectively include spatial correlation. We report on the development of a spatial back-propagation neural network (S-BPNN) model designed specifically to make such correlations implicit by incorporating a spatial lag variable (...

Cellular automata (CA) are effective tools for simulating urban dynamics. Coupling top-down and bottom-up CA models are often used to address macro-scale demand and micro-scale allocation in the simulation of urban dynamics. However, those models typically ignore spatial differences in terms of the coupling process between macro-scale demand and mi...

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 macr...

Urban form characterizes the spatial structure of fixed elements within a city, which affects daily life and has significant influence on environmental sustainability. Measuring the spatiotemporal characteristics of an urban form and its relationship with sustainable development is the basis of urban planning. Taking 27 large cities in the United S...

The scale effects of the spatial autocorrelation (SA) measurement has been explored for decades. However, the effects of the data aggregation levels and spatial resolution on the SA measurement are often confused. Whether the two types of scale effects are the same is still unclear and requires further investigation. We retrieved the land surface t...

Urban land use and transportation are closely associated. Previous studies have investigated the spatial interrelationship between street centralities and land use intensities using land cover data, thus neglecting the social functions of urban land. Taking the city of Shenzhen, China, as a case study, we used reclassified points of interest (POI)...

Though it is recognized that meteorology has a great impact on the diffusion, accumulation and transport of air pollutants, few studies have investigated the impacts on different-sized particulate matter concentrations. We conducted a systematic comparative analysis and used the framework of generalized additive models (GAMs) to explore the influen...

The spatial relationship of newly grown urban patches to existing urban areas lies at the core of understanding the properties of urban expansion dynamics. Some existing landscape metrics have been used to identify patch expansion types, i.e., infilling, edge-expansion and outlying, capturing the evolution process of urban expansion patterns based...

Numerous studies reveal that urban favorable amenities potentially contribute to housing prices, but we still lack proper indices to quantify intangible urban disservices and lack the understanding of their economic effects. We attempt to develop remotely sensed indices to reflect these unfavorable and intangible urban disservices. Taking Wuhan in...

Many existing gradient analysis methods are arbitrary or too simple in gradient partitioning and unsuitable for cities with irregular forms. We propose an improved gradient analysis method with urban structural features as spatial constraints to properly partition an urban area into more homogeneous buffers. Taking the Wuhan metropolitan area in Ch...

Fine particles (PM2.5) and coarse particles (PM2.5–10) are generally produced by different sources, so the PM2.5/PM10 ratio reveals characteristics of particle pollution. The ratio can be used to characterize the underlying atmospheric processes and evaluate historical PM2.5 pollution in absence of direct measurements. However, application of the r...

PM2.5 has become an increasing public concern recently because of its visibility reduction and severe health risks. For the whole year of 2013, hourly PM2.5 data of 496 monitoring sites scattered in 74 cities of China are collected to analyze temporal and spatial variability of PM2.5 concentration. Different temporal scales (seasonal variation, mon...

Abstract: Air pollution is one of the key environmental problems associated with urbanization and land use. Taking Wuhan city, Central China, as a case example, we explore the quantitative relationship between land use (built-up land, water bodies, and vegetation) and air quality (SO2, NO2, and PM10) based on nine ground-level monitoring sites from...