Fig. 2: The Kernel density estimation of ecological civilization construction efficiency in China.

The non-parametric Kernel density function with normal Gaussian distribution was used to continue exploring the clustering differences in the evolution of ecological civilization construction efficiency over time in each province and city. Five years, 2000, 2005, 2010, 2015, and 2020, were the observation time points for kernel density estimation to obtain the distribution at different time points.