Extraction and Evolution Analysis of Urban Built-Up Areas in Beijing, 1984–2018

Abstract

Accurate extraction of the boundaries of urban built-up areas (UBA) based on remote sensing and GIS technology is extremely important for predicting urban spatial evolution. Therefore, this study proposes a method for extracting urban built-up areas based on the impervious surface aggregation density (ISAD) of an object and uses the long-time series of the built-up area extraction results to analyze the spatial and temporal evolution characteristics of Beijing cities. The results show that the precision for extracting UBA using this method is 91.3%, which is better than that of existing methods based on supervised classification. The extraction results can also accurately depict the urban form and maintain the integrity of the built-up areas. Built-up areas in Beijing expanded from 1984 to 2018, with the most significant expansion in 2014–2018. In these 5 years, the expansion speed and intensity of Beijing respectively reached 270.70 km2/a and 1.65%, which were 2.43 times that of the entire research period. Built-up areas in Beijing have been expanding past their original limits over time in a ‘centralized concentric circle’ expansion model. The focus of the UBA moved northeast by 11.56 km. In the past 35 years, the contours of Beijing’s urban borders have become increasingly complex, and the spatial form of built-up areas has become increasingly discrete. The analysis of the spatial evolution of UBA is beneficial for more sustainable, compact and coordinated urban development.