Socioeconomic and spatial segregation informs who benefits from urban growth and who bears its environmental and social costs. In this issue, we explore how infrastructure, labor markets and global policies actively reshape these divides. From the early maps of Park and Burgess1 to the stark portraits of American Apartheid2, cities have been read through the lines that separate groups in space. The articles in this issue show that those lines are drawn not only by where people live but also by how infrastructure routes, labor markets and global initiatives allocate clean air, access and recognition. We move beyond the residential map to the everyday systems that make segregation durable — and sometimes visible in new ways. In their Article, Zālīte and colleagues trace how the rise of technology work is quietly rearranging ethnic and class boundaries in Tallinn, Estonia. Minority technology workers gain access to higher-income neighborhoods and areas with a mixture of class and/or ethnic identities, whereas minority individuals who work in non-technology fields become more isolated in lower-status districts, which deepens class-based segregation within minority communities even as some ethnic divides narrow. Urban infrastructures often promise integration — connecting regions, equalizing access and sharing the benefits of growth. An Article by Liu and colleagues shows a more troubling reality: China’s high-speed rail network improves air quality and public health more in urban areas than in nearby rural zones, which widens the urban–rural gap in pollution and cardiovascular mortality. Rural air pollution is often overlooked: their analysis of firm-level waste gas emission, satellite-based particulate matter and health outcomes reveal that rural areas are at least as polluted as cities, but benefit less from infrastructure-driven improvements. These unequal gains are linked to a redistribution of resources and economic activity towards urban cores, which amplifies environmental injustice and reinforces patterns of