In detail, there was a trend of annual expansion from 1990 to 2009, and a clear trend of contraction from 2009 to 2019, especially in the eastern part of Chaoyang and the northern part of Haidian.
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Spatio-temporal evolution characteristics analysis and optimization prediction of urban green infrastructure: a case study of Beijing, China.
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The sentences
In the time series of the study, the background area showed a trend of "expansion followed by contraction" centered on the main urban area.