A. in twelve years; B. in 2006; C. in 2007; D. in 2008; E. in 2009; F. in 2010; G. in 2011; H. in 2012; I. in 2013; J. in 2014; K. in 2015; L. in 2016; M. in 2017. (The vector data of Chinese administrative divisions were provided by CNNDS. Figure 2 was created for this manuscript using ArcGIS.).</p