“Clearer” or More “Blurred”? The Evolution of Urban–Rural Boundaries Since the Proposal of Urban–Rural Integrated Development: A Case Study of Zhengzhou

As China’s urban–rural integrated development strategy advances, traditional urban–rural boundaries are undergoing rapid restructuring. However, it remains unclear whether these boundaries are becoming distinct through factor flow or blurring due to urban–rural functional coupling. To address this, this study examines the dynamic evolution of boundaries across three core dimensions—population, land, and function—to evaluate the efficacy of integration. We employ the Land Continuity Index, POI Diversity Index, and Gaussian Smoothing Index to characterize transitions in land use structure, spatial functional complexity, and population gradients, respectively. Additionally, a comprehensive Urban–Rural Fuzziness Index (URFI) is developed to quantify boundary blurring trends. Results indicate that Zhengzhou’s urban–rural boundaries exhibit a sustained weakening trend. Notably, changes in functional and population dimensions significantly outpace the land dimension, identifying functional urbanization and population mobility as the primary drivers of this blurring. Consequently, the URFI serves as a robust indicator of integration effectiveness. Overall, boundary blurring is not merely an external manifestation of urban expansion but a profound outcome of factor reorganization, spatial optimization, and the reshaping of urban–rural relationships. This study provides a novel quantitative tool for assessing policy effectiveness, offering both theoretical insights and practical implications for understanding urban–rural integrated development.