## 4 Discussion  
### Differences in the Expansion of the Lanxi Urban Cluster  
From a land use perspective, the expansion of the Lanzhou-Xining urban agglomeration reflects the typical characteristics of urbanization. During the study period, urban land use increased significantly, with this growth trend becoming more pronounced following the establishment of the Lanzhou-Xining urban cluster. [PERSON] et al. found that from 2000 to 2015, the annual growth rate of regional urban land area reached 7.2%, exceeding the national average [67]. [PERSON] et al. indicated in their study that the land in the Lanzhou-Xining urban agglomeration primarily transitioned from green ecological space and agricultural production space to urban construction land, rural living space, and industrial and mining construction land, which is consistent with our research [68]. Moreover, the increase in urban construction land was mainly concentrated in areas such as Lanzhou [68]. Rapid urbanization drove the transformation of land use and accelerated economic restructuring and social development in the region, positioning the Lanzhou-Xining urban cluster as a key engine of regional development. [PERSON] et al. 's research further indicates that during the  
Figure 7: Urban expansion occupies various types of land area (km\({}^{2}\)). process of coordinated urban development within the Lanzhou-Xining urban cluster, the strength of connections between cities in terms of industry, transportation, and information networks has significantly increased [69]. This increasingly close urban linkage has injected strong momentum into the development of the Lanzhou-Xining urban cluster, forming a mutually beneficial regional development network. The improvement of transportation infrastructure, particularly the expansion of highways and railway networks, has facilitated the efficient flow of goods and human resources within the region and enhanced economic interaction and cooperation between cities. Additionally, the construction and upgrading of information networks have further promoted the sharing and exchange of information within the urban cluster, boosting the overall region's competitiveness and sustainable development capabilities. During the expansion of the Lanzhou cluster, several cities, such as Lanzhou, Baiyin, and Xining, expanded significantly more than other cities did. Previous studies have shown that these cities were originally relatively developed, with relatively flat terrain and well-developed infrastructure [70; 71; 72]. As urban clusters develop rapidly, well-developed infrastructure makes life more convenient, attracting more people [73]. [PERSON] et al. analyzed the cities in the Lanzhou-Xining region from the perspective of urban transportation networks and urban vitality, finding that high urban vitality is mainly concentrated in areas like Lanzhou and Xining [74]. Their investigation revealed that urban vitality is closely linked to urban transportation. Lanzhou, Baiyin, and Xining have relatively advanced transportation networks, including highways, railways, and air routes, which can support large-scale population movement. As the population begins to flow, the city's economy is driven, and urban expansion follows. These cities also possess abundant educational and medical resources. High-level educational institutions and medical facilities attract more people to settle and work. Furthermore, Lanzhou, as the provincial capital, and Xining, as the gateway city to the Qinghai-Tibet Plateau, have political, economic, and cultural significance that brings more development opportunities and resource allocation. These factors collectively promote the rapid expansion of these cities. [PERSON] et al. confirmed this viewpoint in their paper \"Spatio-temporal Difference Analysis of Land Use Efficiency in Lanyi Urban Agglomeration Based on the SBM-Undesirable Model\" [75]. In contrast, other cities in the Lanyi urban cluster, such as Linxia and Haidong, do not have these conditions.