How does spatial expansion of higher education affect urban innovation? Regional evidence for Yangtze River Delta, China

In the context of the knowledge economy, higher education has increasingly functioned as a critical spatial infrastructure for regional innovation through human capital formation, knowledge production, and institutional coordination. While higher education expansion (HEE) has been widely implemented to enhance innovation capacity, existing studies have largely examined its average effects within administrative boundaries, paying limited attention to spatial spillovers, nonlinear effects, and metropolitan heterogeneity. Thus, this study aims to systematically investigate the spatial mechanism through which HEE affects urban innovation from a geospatial perspective. Focusing on 41 cities in China’s Yangtze River Delta from 2001 to 2022, we construct a multidimensional urban innovation index based on a patent citation network and employ spatial econometric models to capture intercity interactions. We find: (1) HEE promotes urban innovation. Quantity shows linear positive effects, while quality exhibits an inverted U-shape relationship; institutional factors play critical roles. (2) Spatial spillovers are significant. Quantity expansion generates cross-regional positive spillovers, while quality improvement enhances local innovation. Spillover mechanisms gradually evolved from knowledge diffusion to institution-driven mobility. (3) Metropolitan structure shapes significant heterogeneity. These findings position higher education as a dynamic spatial infrastructure for innovation and offer theoretical and policy insights for fostering coordinated, cross-regional innovation under fragmented spatial governance.