Spatiotemporal Evolution and Multidimensional Synchronicity of Cultivated Land Use Transition: Evidence from the Spatial–Functional–Modal Triad in the Nanjing Metropolitan Area, China

Rapid urbanization can shrink and fragment cultivated land while raising agricultural productivity, creating mismatches among spatial configuration, functional performance, and management modes. These dimensions are rarely assessed in a unified, value-neutral framework. We developed a Spatial–Functional–Modal (SFM) framework to evaluate multidimensional synchronicity in 46 county-level units of the Nanjing Metropolitan Area, China, using Period 6 data spanning 2000–2022. We combined 18 entropy-weighted indicators with coupling and coupling coordination degree (CCD) models at county and municipal scales. Regional SFM-CCD rose from 0.304 to 0.327 but remained in the model-defined near-misalignment category, while average coupling declined from 0.747 to 0.740. All pairwise CCDs increased, but coupling trajectories differed: spatial–functional coupling weakened, spatial–modal coupling diverged between Jiangsu and Anhui, and functional–modal coupling strengthened. Anhui’s SFM-CCD increased more consistently and surpassed Jiangsu in later years. Nanjing remained a relative synchronicity trough, reflecting weaker alignment among normalized dimensions rather than lower absolute agricultural capacity. Alternative weights and ±10% and ±20% perturbations largely preserved relative rankings and the overall temporal pattern, but absolute values and categories remained method-sensitive. The framework diagnoses asynchronous transitions and can inform differentiated governance in other rapidly urbanizing regions.