SCOT: Multi-Source Cross-City Transfer with Optimal-Transport Soft-Correspondence Objectives

Cross-city transfer leverages labeled data from well-instrumented cities to improve prediction in label-scarce ones, but remains challenging when cities adopt incompatible partitions with no ground-truth region correspondences. Even with expressive GNN encoders, transfer quality varies dramatically across methods sharing nearly identical backbones---indicating that alignment design, not encoder capacity, is the binding constraint. Existing paradigms exhibit complementary failure modes: heuristic anchor matching collapses to hubness under unequal partitions, while distribution-level matching over-mixes embeddings under heterogeneity. Both stem from a single missing primitive---explicit, mass-controlled soft correspondence between unequal region sets. The challenge intensifies in multi-source transfer, where independent source-to-target alignments yield conflicting gradients and source domination. We propose SCOT, which adapts entropic OT to this regime through three application-specific designs: an OT-weighted contrastive objective that resolves the geometric--semantic tension, a one-sided cycle regularizer respecting the rectangular $n_s\!\neq\!n_t$ geometry, and---as our central contribution---a shared prototype hub coordinated through balanced entropic OT under a target-induced prior, bypassing the source-selection problem in label-scarce regimes. Across real-world cities and tasks, \scot consistently improves transfer accuracy, achieving 5--50\% relative MAE/MAPE reductions over the strongest baseline, with learned couplings and hub assignments quantitatively confirming that the diagnosed failure modes are resolved.