Ports are clearly demarcated structures on land and water. They are fenced in, easily recognizable on satellite and orthophoto images, and they have specific functions. This apparent clarity of ports, their function and outline, in relation to nearby urban and rural areas, becomes more complex when explored through the lens of land use, that is the existing and planned future functional dimension or socio-economic purpose of the land. In contrast to urban and rural areas, where land use has been mapped and defined for centuries, the use and function of land and water in port areas has long been multifunctional and not defined on land use maps. This raises questions about the role and understanding of port territory in relation to neighboring spaces, past, and present. This article first defines land use and describes its historical development. Scholars from various disciplines, including geographers, planners, and economists, have addressed the issue of land use in port areas. Land use patterns have emerged over time and are based on earlier demarcations of port areas and distinctions between port and city. As shown by the historical port city borders in Hamburg, Rotterdam, and Koper, these delimitations can change over time, by location and by function. The land use register has only recently been harmonized at the European level. European and national registers distinguish existing and planned land use in port areas differently. Mixed uses prevail in new port interventions, creating a new kind of permeability or porosity; that is, areas where port, urban and rural functions merge. New land use porosity is a particular state of land use (on both sides of the boundaries of port areas) that goes beyond the physical boundaries marked by fences. Land use porosity effectively creates land use continuity, a functional porosity that serves as a hidden blueprint for future planning. Understanding land use porosity can provide a foundation for novel approaches to the development of transition strategies that are needed to address contemporary challenges, including climate change and sea level rise, digitization, and new work and life practices in port city regions. In conclusion, we note that due to the porosity of land use patterns, the separation between the present port and the city is beginning to crumble. However, this process has yet to be made fully visible and used as a basis for design. [ABSTRACT FROM AUTHOR]