Acta Geographica Sinica ›› 2022, Vol. 77 ›› Issue (11): 2687-2702.doi: 10.11821/dlxb202211001

• Land Use/Land Cover Change •     Next Articles

Analysis of urban expansion and fractal features in global 33 megacities from 2000-2020

HOU Yali1,2(), KUANG Wenhui1, DOU Yinyin1()   

  1. 1. Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2021-10-09 Revised:2022-10-23 Online:2022-11-25 Published:2022-12-27
  • Contact: DOU Yinyin;
  • Supported by:
    Strategic Priority Research Program of Chinese Academy of Sciences(XDA20040403);Strategic Priority Research Program of Chinese Academy of Sciences(XDA23100201)


The ultimate form of urbanization is the megacity, which is the typical form of urban structural characteristics and population agglomeration effects. However, the comparative studies on the urban form and expansion patterns of megacities worldwide are still insufficient. This study first analyzed the spatiotemporal changes of land use in megacities based on the Global Urban Land Use/Cover Composites with a 30 m spatial resolution (GULUC-30) by using the method of urban expansion intensity differentiation index (UEDI). Then, the fractal structure and expansion patterns of megacities were investigated using the area-radius model. Finally, urban land use efficiency was assessed through a linear relationship between urban land area and its interna population. The findings include: (1) Southeast Asia and China had experienced the most dramatic urban land expansion (3148.32 km2 and 5996.26 km2) over the last 20 years, along with the average UEDI of both greater than 3. (2) In 2000-2020, morphological characteristics and sprawl patterns of megacities developed toward greater intensification and compactness, with the mean radial dimension increased from 1.54 to 1.56. Meanwhile, radial dimension difference showed a year-by-year decreasing trend, and the intra-city structure showed integration. (3) In 2020, urban land use efficiencies in both North America and Europe were low, with urban land area to its population ratio coefficients ranging from 0.89 to 4.11. On the contrary, high values happened in South Asia and Africa, from 0.23 to 0.87. Spatial patterns and morphological changes in megacities provide important reference values for the intensive utilization of urban land and its sustainable development. Controlling the scale of megacity expansion and promoting the balanced exploitation of urban land are the essential ways for building resilient cities and sustainable urban planning.

Key words: megacities, radial dimension, radial dimension difference, urban expansion, urban land use efficiency