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. 2020 Oct 23;11:5366. doi: 10.1038/s41467-020-19158-1

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a Distribution of the 841 large cities at four different levels of the population density (PopD, unit: 1/km²) in 2015. D1: 0 < PopD ≤ 1K, blue points; D2: 1K < PopD ≤ 5K, green points; D3: 5K < PopD ≤ 10K, orange points; D4: PopD > 10K, magenta points. b Bars are the percentages of the 841 large cities for four PopD levels in 2015 at four economic levels. Error bars show SEM for each economic level. c Relationship between PopD in 2015 and the BUA expansion from 2001 to 2018 of the 22 large cities with population growth larger than 2M. YRD Yangtze River Delta, PRD Pearl River Delta. The size of the dots refers to the population growth at different levels.