Research on the Interactive Relationship of Spatial Expansion between Estuarine and Coastal Port Cities

In both developed and developing countries, port-city relationships have always attracted much attention. However, in the port–city interface, views differ as to whether the port drives the city or vice versa. The combination of remote sensing data and geospatial big data (point of interest) has provided a favorable solution. Taking the typical estuarine and coastal port cities in China’s coastal zone as an example, this study examines the following contents based on the port–city interface: the formation age of urban built-up areas and port areas on both sides of the port–city boundary; interaction between port and urban built-up areas; and the distribution of urban functional areas outside the port. Results show that the degree of spatial integration in estuarine port cities is higher than that of coastal port cities and that in the past 30 years, the expansion of ports has led to the expansion of cities. This expansion is port- and sea-oriented, and the expansion direction of the port city is consistent. On the port–city interface, the estuarine and coastal port cities form different urban regional structure modes. Aside from enriching literature on the port–city relationship, this study provides a reference for the spatial planning and transformation of ports and cities in the future.