Urban activities are a significant source of global carbon emissions. Balancing economic development and environmental protection during urban construction and development has become a common concern worldwide. The urban form structure, as the spatial foundation of urban activities, is critical for both current and future urban development. In this study, an urban economic activities perspective is taken to examine the relationship between the urban form structure and carbon emission efficiency in 63 prefecture-level cities within China’s three major urban agglomerations from 2013 to 2022. Two dimensions are considered: land resource development and the urban spatial layout. The research findings indicate that (1) the built-up areas of the three major urban agglomerations in China generally exhibit a pattern of “core cities expanding outwards and peripheral cities emerging sporadically”. (2) Various urban form structure indicators have different effects on carbon emission efficiency, with interaction detection via geographic detectors showing a dual-factor enhancement effect. (3) Urban form structure influences carbon emission efficiency through the mediating pathway of economic agglomeration. This study enriches empirical research on the impact of the urban form structure on carbon emission efficiency from an economic activities perspective and provides empirical evidence for urban spatial planning and achieving sustainable development.

Digital economy industrial agglomeration is significant for economic development and the realization of “dual carbon” goals. Based on the point of interest (POI) data of digital enterprises, this study uses kernel density estimation, a fixed-effect model, a spatial Durbin model, and other methods to analyze the spatiotemporal characteristics of digital industrial agglomeration in the four major urban clusters along the east coast of China and examines their corresponding influence on carbon emissions, including spatial spillover effects. The key conclusions are as follows: First, digital industry development and the degree of agglomeration display increasing trends. The degree of agglomeration is high in the east and low in the west, with high-value areas characterized by core prominence and orderly expansion. Second, a negative relationship is observed between digital industrial agglomeration and carbon emissions, with specialized agglomeration significantly reducing carbon emissions, while diversified agglomeration has a weaker effect. Third, the influence of digital industrial agglomeration on carbon emissions exhibits spatial spillover effects with heterogeneity. These findings provide a theoretical basis for the development of regional digital industry agglomeration and have significance as a reference for the formulation of energy conservation and carbon-reduction policies.