## 4 Experimental Results and Analysis
### Experimental and Results Analysis
After merging and de-duplication, 12,921,707 PS points were retained, which accounted for approximately 93.2% of the original PS candidate points. However, the initial merging results exhibited significant systematic deviations in both the deformation rate and elevation residuals (Figure 7a). After correction using a weighted least squares adjustment, the stitched results (Figure 7b,c) demonstrate that the adjustment model effectively eliminated the systematic bias between sub-blocks. The traditional stitching method (Figure 7b) refers to a block-merging approach that directly combines adjacent sub-blocks without analyzing the connectivity relationships or preserving isolated PS clusters. This method enforced a full-rank coefficient matrix by retaining only the largest connected domain (157 sub-blocks), which inevitably excluded fragmented components beyond this domain. As a result, PS point information from 45 sub-blocks (22.3% of the total) was discarded, and thus, only 94.4% of the PS points were retained compared with the proposed method. These excluded points predominantly corresponded to non-urban areas (e.g., scattered villages and suburban zones), which led to critical gaps in the local deformation monitoring. In contrast, the proposed stitching method (Figure 7c) utilizes global connected component identification and regionally independent adjustment strategies. By analyzing graph-based topological relationships and performing weighted least squares adjustments  
Figure 6: Sub-block connectivity map. (All sub-blocks in the same connected component are shown in the same color, labels 1���❝�\(-\)�\(\dot{\)}\) represent the color table for the 9 connected components, gray diagonal hatching regions are sub-block overlap areas, black dots are sub-block centers, and lines between the endpoints indicate valid overlap areas between sub-blocks). for each connected component, this approach ensured complete retention of the PS points from all 202 sub-blocks (Table 1). A comparison shows that the traditional stitching method discarded 5.6% of the PS points outside the largest connected domain (the area outside the red rectangle in Figure 7c), corresponding to scattered villages and suburban areas at the city's edge, which led to the loss of crucial local deformation monitoring information. By incorporating connected component identification and regional adjustment, the proposed method effectively mitigated this issue, and thus, preserved the deformation signals in peripheral regions and enhanced the completeness and reliability of the global monitoring results. The final results are shown in Figures 8 and 9, where the PS points in the areas with man-made features are fully covered, and the overall point count reached the ten million level, which supported refined deformation analysis for sparse village areas or individual buildings. The global elevation residuals were concentrated in the range of [\(-\)30 m, 110 m], which was consistent with the actual building height distribution, with the InSAR monitoring points densely distributed along the contours of high-rise residential areas and large single buildings (Figure 8). The global deformation rates were concentrated in the range of [\(-\)10 mm/y, 4 mm/y]. The severely subsiding areas (deformation rate \(\leq-\)10 mm/y) were mostly concentrated in self-built houses in urban villages, construction areas, riverbank protections along the Min River, and major roads. Most areas had deformation rates around 0 mm/y (Figure 9). Figure 7: Sub-block PSinSAR results (the red rectangle indicates the distribution of sub-blocks in the largest sub-connected domain). **(a)** Elevation residuals of the sub-blocks before stitching. **(b)** Elevation residuals using the traditional stitching method. **(c)** Elevation residuals using the proposed stitching method. **(d)** Deformation rates of the sub-blocks before stitching. **(e)** Deformation rates using the traditional stitching method. **(f)** Deformation rates using the proposed stitching method.