## 6 Conclusions  
The conclusions and implications of the research results indicate the following:  
1. The expansion speed of urban built-up land showed a trend of slowing down, and the UBLGUE was diverse since Central China Rise. According to the characteristics of time differentiation, the average UBLGUE values in the CPUA display fluctuating stage characteristics ranging from 0.7802 to 1.1694 in 2003-2020. The average UBLGUE values fluctuated in the CPUA from 2003 to 2020. By 2015, the UBLGUE value had reached the topmost part of the curve. UBLGUE values are located in the middle-high-level range, meaning that the UBLGUE of the cities is insufficient and in an inefficient state.
2. The UBLGUE of the CPUA is characterized by spatial imbalance, and the efficiency gap among cities in the CPUA is large and continues to expand since Central China Rise. The characteristics varied significantly at different prefecture-level cities. Specifically, there are certain geographical differences and significant spatial polarizations in terms of UBLGUE in 2003 and 2020. Cities that have the high- and medium-high-efficiency levels were distributed in the southeastern CPUA in 2003. In 2020, most cities with higher level efficiency were located in the south-central region of the CPUA, whereas cities with lower UBLGUE were distributed in the north-central region of the CPUA. The policymakers of these cities should formulate different UBLGUE standards to limit, adjust, and optimize the regional land use structure according to the urban functional orientation.
3. With respect to the influence mechanism of UBLGUE, regional differences in UBLGUE are the result of complex interweaving socioeconomic factors in 2003-2020. Specifically, the main factors influencing the spatial-temporal differentiation of the UBLGUE in the CPUA were economic development. UBLGUE has strong economic attributes and is positively promoted through economic development. Energy consumption intensity and foreign direct investment have a significant negative effect on UBLGUE, whereas energy consumption intensity is the main factor that restricts urban built-up land efficiency in the CPUA.  
Y.G.: writing--original draft, software, and data curation; Y.S.: data curation; K.L. and T.W.: methodology; Y.H.: funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Henan Provincial Soft Sciences Research Plan Project (No. 232400410095), the Support Doctor Program in Henan Polytechnic University (No. SKB2023-02), the Support Program for Innovative Talents in Philosophy and Social Sciences in Universities of Henan Province (No. 2023-CXRC-05), the Special Project on the Inheritance and Development of Excellent Traditional Chinese Culture in Universities of Henan Province (No. 2023-WHZX-28), and the Henan Provincial Philosophy and Social Science Planning Project (No. 2023 CSH029).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Acknowledgments:** The authors would like to thank the editors and reviewers for their constructive suggestions.  
**Conflicts of Interest:** The authors declare that they have no conflicts of interest or personal relationships that could have appeared to influence the work reported in this paper.