Fig. 5

Geographic location of all PTB reporting facilities in Sichuan Province, China. Black, blue, green, red, and yellow points represent facilities that started reporting before and in 2005; in 2006–7; 2008–10; 2011–14; and 2015–17, respectively. Background color represents population density in 2010 [33], and heavy and light black lines represent prefecture and county boundaries, respectively. The boundary of Chengdu Prefecture, containing Sichuan’s capital, is delineated in red. Inset histogram shows the count of facilities that began reporting each year. Publically available administrative boundaries used in this visualization were obtained from China’s National Earth System Science Data Sharing Infrastructure [24]