## 6 The Case (Xiong'an New Area, China)
### Suitability Evaluation  
Numerous researchers have applied a variety of approaches to GSEUUS in the Xiong'an New Area from different viewpoints. [PERSON] [150] employed the AHP-CIM to examine the geological viability of shallow, sub-deep, and deep UUS. [PERSON] et al. [2] proposed a combined evaluation method that integrates the EWM and CRITIC weighting, creating an evaluation index system for GSEUUS. This method factors in the variability, interrelations, and comparative strengths of the evaluation indicators, leading to a more logical and scientifically sound determination of weights. [PERSON] et al. [146] developed a CM for GSE in the Xiong'an New Area, grounded in the EWM analysis method, while comprehensively considering variables that affect urban development suitability, including geological conditions, groundwater status, and environmental geological concerns (Figure 10). This methodology improves the quantification of the weights of evaluation factors, enhancing both the accuracy and dependability of the evaluation outcomes.  
Through a scientific assessment of geological factors, the safety, sustainability, and rationality of developing UUS can be assured, while it is possible to reduce the potential risks linked to geological aspects [5,25]. An GSE clarifies the geological conditions and developmental potential across various areas, offering scientific insights for the spatial organization and functional zoning of the Xiong'an New Area, thereby promoting harmonious regional growth. This method aids in preventing unrestrained development and illogical utilization of UUS resources, which in turn supports the sustainable advancement of Xiong'an New Area and achieves equilibrium among economic, social, and environmental benefits. By encouraging the thoughtful development and use of UUS, the urban resilience of Xiong'an New Area can be strengthened, leading to the enhanced capacity of the city to manage natural disasters and emergencies, thereby ensuring safety and stable operations. As a nationally designated new area, the planning and development of Xiong'an New Area is of considerable significance. The outcomes of this research not only bolster the planning and construction endeavors of Xiong'an New Area but also offer valuable insights and models that can inform the development and utilization of UUS in other urban areas.  
Figure 9: Proposed map and location of UUS development and utilization in Xiong’an new area [66].  
SEA has been effectively applied in the development of the Xiong'an New Area. The planning of its UUS adheres strictly to SEA principles. It dynamically integrates geological suitability evaluation indicators, such as soil layer bearing capacity and sand layer liquefaction index, with environmental strategic goals, including carbon neutrality and the protection of biological corridors. This approach has led to the construction of the world's first multi-objective optimization model that encompasses 'geology-ecology-energy.' [158,159] In subsequent work, the weight ratio of geological factors to environmental factors should be dynamically adjusted. For ecological redline zones, it is essential to significantly elevate the priority of environmental factors. When evaluating the environmental carrying capacity of the Xiong'an New Area, it is crucial to consider not only conventional conditions and ecological redline zones but also the impact of inter-basin water transfer.