The transition towards smart cities demands a multifaceted approach, which becomes particularly challenging in port cities, where urban life intersects with global logistics. While ports serve as critical logistic nodes, they hold the potential for diverse urban uses beyond mere ship traffic. This study investigates the integration of physical and digital infrastructures in port cities, focusing on the area where urban space expands towards RoPax terminals that combine wheeled cargo and passenger transport. The study is designed as a case study of a Baltic Sea port city undergoing significant infrastructural changes, including the construction of a new passenger terminal and rearrangement of the area surrounding the port. We explore the development of digital infrastructure to facilitate the coexistence of a liveable city and efficient transport connections. Our analysis is based on the dimensions of a smart city and related interfaces. The findings identify key digital interfaces between the city and its port, highlighting five types of such interfaces and the unique challenges and opportunities in balancing the smart city goals of urban and port authorities. This study contributes to the literature on smart cities by demonstrating the critical role of ports in the formation of smart cities, with implications for similar urban contexts.