Objective The Grand Canal is an important linear corridor gathering plenty of materials and intangible cultural heritage. In recent years, cities along the Grand Canal have, under the guidance of the basic construction idea of "control and protection, theme display, integration of culture and tourism, and traditional utilization", successively carried out the construction of national cultural parks, for which systematic planning and design methods and canal culture connotation interpretation and expression methods are urgently needed as support. In the previous research on cultural heritage conservation, the application of the narrative space theory and relevant methods focuses on the integration and law analysis of narrative resources and the planning and design of spatial patterns, with cultural connotation being implied in spatial structure. However, the significance of cultural interpretation and transmission is emphasized under the new system of national cultural parks. In addition to solving the basic problems of boundary delimitation and spatial structure organization, it is also urgent to maximize the preservation of the integrity of cultural elements based on the spatial structure and resource organization of national cultural parks, and strengthen tourists' cultural perception and cultural cognition. Besides, the application of new technologies has become the key to broadening cultural transmission to narrative expression.

Methods This research takes the six districts in Tianjin (Nankai District, Heping District, Hebei District, Hexi District, Hedong District and Hongqiao District) as research area, the period from Yuan Dynasty to the modern times (1271–2020) as research time range, and the cultural heritage surrounding the Grand Canal in Tianjin as research object. The research screens 224 narrative elements related to the Grand Canal and, according to the classification standard adopted, has them divided into artificial, event and human elements to form a database on the narrative space of the Grand Canal. Based on the aforesaid database, the research has the narrative elements screened abstracted into narrative element points with spatial information on the GIS platform by the kernel density analysis method, with the spatial positions of these points being observed in point mode. After that, the research verifies the changing trend of the spatial correlation between narrative element points and the Grand Canal by the multi-distance spatial clustering analysis method (Ripley's K), explores the distribution rule of narrative elements in narrative space as time changes from the perspective of the overall situation, and reveals the process of and reasons for the spatial evolution of the Grand Canal. Finally, the research has each element adjusted into a unified parameter standard to obtain the overall narrative space structure and the distribution characteristics of spatial narrative elements and, using the reclassification technology, defines the spatial aggregation range of narrative elements at multiple levels to determine the core area and narrative spatial structure of the Grand Canal National Cultural Park in Tianjin.

Results The results show the evolution characteristics of the narrative space structure of the Grand Canal at each historical stage and under each narrative theme. Through analysis, the research has the following four findings. 1) Historical continuity. Many narrative elements have always played an important role of cultural carrier. With the development of the times, these narrative elements have already bred new cultures through constant cultural integration and inheritance. 2) Element aggregation. Based on the integrated development of various narrative elements, the narrative space segment has formed a gathering trend relying on the Grand Canal, with small narrative elements being gathered around key narrative elements. 3) Spatial growth. The event elements change continuously in attribute, quantity, aggregation degree and influence scope, during which the narrative spatial structure is gradually clear, and the characteristics of canal space are gradually distinct, forming a spatial structure with multiple aggregation characteristics such as core, area, axis and node. 4) Segment succession. The narrative space segment has experienced a dynamic process of evolution and replacement. The narrative elements carried at the same spatial position will gradually change with the course of history, and the narrative segment formed as a result of the gathering of the same kind of narrative elements will gradually complete the partial or overall succession with the emergence of new narrative elements and the degradation of old ones.

Conclusion Through the excavation and sorting of the historical data about the Grand Canal in Tianjin, the discrimination of narrative elements and the analysis of spatio-temporal evolution, and the summary of the structural and morphological characteristics of narrative space, this research proposes the canal narrative space structure of "One Belt, Two Cores, Eight Districts and Multiple Points", in an effort to provide cultural value basis for solving such problems as scope determination of the Grand Canal National Cultural Park scenic area, spatial layout structure of the core area, planning of tourist routes and application of digital technology based on the narrative interpretation of the value of cultural heritage, which is exactly an attempt and breakthrough in the exploration and display of the cultural value of the Grand Canal and the optimization of the narrative experience of tourists. This research will contribute to the development of the narrative function of the Grand Canal National Cultural Park, and provide support for the value excavation and interpretation of the inherent cultural heritage of the Grand Canal National Cultural Park in Tianjin.