The accurate extraction of Built-Up Areas (BUAs) is of great significance for analysing urban spatial evolution patterns. In this study, we proposed a new method for high-precision extraction of BUA based on multi-source remote sensing data. Firstly, Built-Up Area Extraction Index (BAEI) was used to preliminarily identify the BUA based on Landsat 8 imagery. Secondly, the Support Vector Machine (SVM) algorithm was used for improving the extraction precision of BUA, whose selected training sample was established on the Nighttime Light (NTL) data. Then, images fusion and continuity correction were carried out. Finally, the Neighbourhood Statistics Analysis (NSA) was used to adjust and remove the part of the non-urban centre which was misjudged as the BUA. Our results show that this method has better performance on both overall accuracy and Kappa coefficient compared with other classic methods, which provides empirical reference for understanding law of land expansion and rational land planning.

High-speed rail (HSR) and aviation have played an important role in shaping urban connections and building urban networks. However, with the continuous expansion of the scale of HSR, the competition between the two has become increasingly fierce, and HSR has gradually been substituted for aviation in some regions. Therefore, based on HSR flow and airline flow data, we depicted the spatio-temporal evolution pattern of China’s urban network from 2017 to 2021 by constructing the HSR–aviation composite network, then identified the spatial scope and network form of the substitution of HSR for aviation through classifying the four types of segments, and analyzed the influencing factors of this substitution effect. The results showed that the spatial form of the HSR–aviation composite network is “spindle-shaped” and has a right-skewness distribution; the spatial scope of HSR completely or partially substituting for aviation is mainly distributed in the “diamond-shaped” space with Beijing–Shanghai–Guangzhou–Chengdu as the apex; and 0–770 km is the absolute advantage distance range of HSR. Moreover, the scale expansion of the composite network, the comparative advantages of HSR in shaping the urban network, the personal travel preference for HSR, and the distance between cities and city attributes are the main factors that make HSR a substitute for aviation.