Browsing by Author "Xu, Gang"

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Characterizing urban expansion combining concentric-ring and grid-based analysis for Latin American Cities
(MDPI, 2021) Wu, Su; Sumari, Neema Simon; Dong, Ting; Xu, Gang; Liu, Yanfang
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 decay of urban elements from city centers. Grid-based analysis partitions a city into regular grids that are used to interpret local dynamics of urban growth. We combined these two approaches to characterize the urban expansion between 2000–2014 for five large Latin American cities (São Paulo, Brazil; Mexico City, Mexico; Buenos Aires, Argentina; Bogotá, Columbia; Santiago, Chile). Results show that the urban land (built- up area) density in concentric rings decreases from city centers to urban fringe, which can be well fitted by an inverse S curve. Parameters of fitting curves reflect disparities of urban extents and urban form among these five cities over time. Grid-based analysis presents the transformation of population from central to suburban areas, where new urban land mostly expands. In the global context, urban expansion in Latin America is far less rapid than countries or regions that are experiencing fast urbanization, such as Asia and Africa. Urban form of Latin American cities is particularly compact because of their rugged topographies with natural limitations.
A Geospatial Approach to Sustainable Urban Planning: Lessons for Morogoro Municipal Council, Tanzania
(Sustainability, 2019-11-19) Sumari, Neema S.; Xu, Gang; Ujoh, Fanan; Korah, Prosper I.; Ebohon, Obas J.; Lyimo, Neema N
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.
On the absurdity of rapid urbanization: Spatio-temporal analysis of land-use changes in Morogoro, Tanzania
(Cities, 2020-07-07) Sumari, Neema S.; Cobbinah, Patrick Brandful; Ujoh, Fanan; Xu, Gang
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 classifier, and spatial analysis were adopted to analyze Multi-temporal Landsat images obtained through the Google Earth Engine platform to quantify the spatial and temporal distribution and pattern of land-use change. Findings from this research show that Shannon's entropy values for MUM increased from 0.522 in 2000, to 0.761 in 2007, and to 0.901 in 2016 with the urban land cover recording a considerable and consistent increase. Similarly, the municipality's annual rate of change in population decreased from 4.17% in 1967 to 3.81% in 2016, and is estimated to rise to 4.54% by 2030 with a corresponding population of 25,262 in 1967 and 622,000 in 2016. From the results, the rate of population growth is not commensurate with the rate of spatial expansion, as the spatial extent is more than twice the population growth. An important contribution from this research relates to the limited attention to the faster rate of urban expansion compared to population growth in African cities; a situation that is inconsistent with sustainable and resilient urban futures. It is recommended that municipal authorities should consider initiatives (e.g., environmental planning models) to reverse the current trend of urban growth in order to improve the health, density, sustainability and resilience of the urban environment.
Urban expansion and form changes across African cities with a global outlook: Spatiotemporal analysis of urban land densities
(Journal of Cleaner Production, 2019-03-27) Xu, Gang; Dong, Ting; Cobbinah, Patrick Brandful; Jiao, Limin; Sumari, Neema S.; Chai, Baohui; Liu, Yaolin
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.