## 5 Discussion  
### Analysis of the Factors Influencing UBLGUE  
Economic growth positively impacts UBLGUE, and this finding implies that higher economic growth leads to higher UBLGUE in general. An increase in economic growth produces a significant driving force for environmental management. Typically, an advanced economy is accompanied by a high degree of city construction, which is often indicated by complete urban functions and benefits, thus affecting the vertical development of land resources. Additionally, the cities in the CPUA exploit the stock of built-up land, rather than expanding built-up land to achieve long-term stable economic growth, given the scarcity and irreplaceability of land, which accelerates urban built-up land intensity and green use efficiency, thus supporting high UBLGUE. Therefore, economic development can strongly force improvements in UBLGUE among the independent variables, which indicates that the government of the CPUA should attach importance to the use of scale economies and spillover effects in order to excavate the potential of urban built-up land resources and achieve optimal resource allocation. The industrial structure has negative influence on UBLGUE, and the negative impact can be ascribed to the two following aspects. First, when the secondary industry development speed exceeds that of the tertiary industry, the rigidity of the low-end industrial structure will increase, and the space for high-value-added industries will be occupied. This pattern is not conducive to promoting a technology-intensive and capital-intensive industrial structure, and it reduces UBLGUE. Second, cities in the CPUA actively accelerate green use transformation and industrial structure adjustments, which decreases the marginal output benefit of built-up land use, resulting in a relative increase in production factor prices (land and capital elements). This imbalance further leads to the industrial structure accelerating the decrease in UBLGUE. On the basis of the above analysis, it is clear that the industrial structure has failed to promote the advancement of UBLGUE. The environmental regulation intensity is negatively related to UBLGUE within the 10% level. This finding implies that a higher environmental regulation intensity has a significant negative role in promoting UBLGUE. Environmental regulation is often ignored by government managers, as it is characterized by large investments, slow effects, and low economic benefits. Advanced environmental regulation can introduce advanced industrial production technologies and reduce the cost of industrial green technology innovation, thereby promoting cleaner production, supporting the governance of pollution at the end of the pipe, and finally reducing pollution and damage. Notably, the role of regulation intensity in promoting UBLGUE is not great, but it is significant. The UBLGUE of the CPUAis still driven by the short-term interest in economic growth associated with traditional high-energy-consuming industries, which largely crowds out the financial investment that should be used for environmental governance. Thus, the environmental regulation intensity support for UBLGUE is insufficient to increase the green transformation of urban built-up land. This finding of energy consumption intensity indicates that a higher energy consumption intensity decreases the improvement in UBLGUE. This negative correlation can be attributed to the following underlying aspects. On the one hand, electric power is currently the main type of energy used for urban consumption, as increasing urbanization leads to the expansion of the scale and functions of cities. Under this energy utilization structure, the sectors with lower built-up land use efficiency cannot be replaced with sectors with high built-up land use efficiency because of the rigid energy system, which prevents the increase in UBLGUE. The empirical results further reveal that energy consumption intensity leads to a decrease in the UBLGUE of a city.