## 3 Results
### Impact of Urbanization on Ecological Quality in Urban Built-Up Area  
Figure 5 displays the location of the core regions and expansion regions in the three study areas, along with the corresponding EQI transitions across different grades. The comparison results reveal that PRD has the largest core region area (5177 km\({}^{2}\), 9.90% of the total land area) (Figure 5c), while CYRD exhibits the highest ratio of expansion areas (approximately 252.9%). Referring to Figure 3, it is evident that urban expansion primarily occurs in two types of areas: the periphery of the urban core region and flat terrains suitable for farming with sufficient water. Figure 5: The spatial location and EQI transfer conditions of urban core and expansion areas in urban agglomerations. (**a–c**) Spatial location of urban core and expansion areas by region. (**d–f**) EQI transfer rate between EQI levels in urban core region of BTH, CYRD, and PRD, respectively. (**g–i**) EQI transfer rate in urban expansion region of BTH, CYRD, and PRD, respectively. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**BTH**} & \multicolumn{4}{c}{**CYRD**} \\
**EQI Level** & **Excellent** & **Good** & **Moderate** & **Poor** & **Bad** & **Total** & **Excellent** & **Good** & **Moderate** & **Poor** & **Bad** & **Total** \\ \hline Excellent & 8800 & 11,033 & 388 & 42 & 0 & 20,263 & 58,071 & 7414 & 510 & 73 & 0 & 66,068 \\ Good & 3925 & 42,199 & 38,536 & 3532 & 20 & 88,212 & 2539 & 48,941 & 51,233 & 7991 & 8 & 110,712 \\ Moderate & 26 & 7527 & 56,607 & 16,217 & 103 & 80,480 & 178 & 1925 & 14,431 & 10,505 & 53 & 27,092 \\ Poor & 0 & 184 & 12,945 & 10,140 & 1676 & 24,945 & 4 & 229 & 1833 & 8661 & 600 & 11,327 \\ Bad & 0 & 0 & 0 & 55 & 343 & 398 & 0 & 6 & 109 & 726 & 256 & 1097 \\ Total & 12,751 & 60,943 & 10,8476 & 29,986 & 2142 & 214,298 & 60,792 & 58,515 & 68,116 & 27,956 & 917 & 216,296 \\ \multicolumn{10}{c}{PRD} \\ EQI level & Excellent & Good & Moderate & Poor & Bad & Total & & & & & & & \\ Excellent & 24,403 & 1025 & 82 & 9 & 0 & 25,519 & & & & & \\ Good & 3379 & 8001 & 2350 & 355 & 0 & 14,085 & & & & & \\ Moderate & 65 & 908 & 5337 & 3110 & 2 & 9422 & & & & & \\ Poor & 0 & 5 & 241 & 3006 & 9 & 3261 & & & & & \\ Bad & 0 & 0 & 0 & 1 & 0 & 1 & & & & & \\ Total & 27,847 & 9939 & 8010 & 6481 & 11 & 52,288 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The EQI transfer matrix for each level from 2001 to 2020 of urban agglomerations. In the core regions of all three urban agglomerations, the main EQI transition between different levels is from \"Moderate\" to \"Poor\" (Figure 5d-f), with the conversion ratios of all \"Moderate\" pixels reaching 91.6%, 74%, and 52.4%, respectively (see Table S2). The expansion regions of all three study areas are experiencing a decline in EQI, with the ratio of expansion areas undergoing EQI decline being approximately 60% for BTH and CYRD and about 40% for PRD (Table S2). The main transition directions are from \"Moderate\" to \"Poor\" and \"Good\" to \"Poor\" (Figure 5g-i). Notably, in 2020, the proportion of pixels with EQI levels of \"Moderate\" and \"Poor\" in all three urban clusters exceeded 90%, with the most pronounced decline observed in CYRD (Table S2). Table 6 depicts the land cover (LC) transition conditions in the three study areas. As depicted in the table, cropland conversion accounted for approximately 90% of the new impervious land area in both BTH and CYRD, while constituting about 78% in PRD. Speculation arises that human activities have altered scattered water systems, wetlands, and lakes around the city through water filling and land reclamation, thereby making water bodies the second most significant source of LC transition for urban built-up areas in 2020 [92]. Upon comparing the results in Table 6, it becomes apparent that pixels witnessing EQI deterioration are essentially aligned with the locations of LC undergoing urbanization-related changes.