Identification and evolution of territorial space from the perspective of composite functions

At present, China is in a stage of unbalanced and insufficient development, in which territorial space with distinctive dominant functions, regional coordination, and reasonable layout, is an important guarantee for the healthy and sustainable development of the national economy and society. However, under the Chinese territorial spatial planning system, the spatio-temporal evolution of spatial multi-functionality has not received much attention, especially in urban agglomerations, which restricts the optimization of territorial space development and protection patterns. Therefore, analysis of the quality, structure and spatio-temporal evolution process of territorial space functions (TSFs). Based on the construction of a theoretical framework of territorial space composite functions, revised night-time light index, agricultural production index, and habitat quality were used to respectively characterize the quality of urban-agricultural-ecological space. Additionally, a coupling coordination degree model and spatial overlay analysis were used to measure the composite level of TSFs, to describe their spatio-temporal evolution characteristics comprehensively, and to summarize the composite mode of TSFs in urban agglomerations. The results demonstrate that from 2000 to 2020, the TSFs center of gravity in the Beijing-Tianjin-Hebei region was in Beijing and Langfang, and the development direction of urban and agricultural space was opposite to that of ecological space. The TSFs composite level demonstrated an overall upward trend, and the level of coupling coordination degree was characterized by a circling spatial evolution from low to high and back to low, along the edge towns, to suburban areas of large cities, to central urban areas of large cities. Overall, urban development and agricultural production functions were strengthened while ecological maintenance function was weakened. The spatio-temporal evolution characteristics of the 27 TSFs composite types were portrayed, indicating that the TSFs had conflicting performance for their scale and composite features for their function, and that the territorial space composite function (TSCF) mainly appeared in suburban areas under the influence of multiple factors. The findings demonstrate a new approach to diagnose TSCF and analyze its spatio-temporal evolution, which can provide a reference for the planning and management of territorial space in urban agglomerations.