"City in the Cloud - Data on the Ground" is a scholarly book that examines the hidden physical infrastructures behind the digital world. Although data is often perceived as intangible, it relies on extensive global networks that encompass the extraction of raw materials, the deployment of thousands of undersea cables, and the ever-growing number of energy-intensive data centers. These infrastructures not only influence global economies and politics but also have profound effects on local communities, ecosystems, and working conditions, which are often rooted in (neo)colonial exploitation structures. The contributions in this volume call for greater transparency, critical awareness, and mindfulness regarding the material foundations of the data economy to enable fairer and more responsible digital futures. The book brings together perspectives from architecture, media studies, technology, art, and political theory, illuminating the fundamental spatial and temporal dimensions of data architecture. It maps the costs of the data economy—ecologically, socially, and politically—and opens new perspectives for reassessing digital infrastructures in the context of planetary resources, justice, and long-term responsibility.