The Deep City project at the Swiss Federal Institute of Technology in Lausanne has, since 2005, been working on an alternative vision for urban planning in which underground resources (water, space, geothermal energy and geomaterials) enter early on in the process of imagining a city’s future . Such a vision is seen as providing an opportunity for sustainable as well as more compact, pedestrian-oriented forms of development through an explicit engagement with underground resources (in particular, space). Mapping is central to this endeavor because it is intended to be the common ground for communication in planning activities and to enable exchange of knowledge between different disciplines. Maps of geological formations and their resource potential are combined with maps of urban morphology, political spatial decisions and economic values, synthesizing this information into an aid for decision-making practices. The map in this context may seem like a passive representation tool for accessing an objective reality waiting to be discovered—but this is wholly inaccurate. In this communication, I highlight the performative nature of the map as a tool for bringing into being a reality—and a knowledge—that otherwise did not exist previously in any ‘objective’ form. I do this by looking at the use of mapping and the underlying method of its production in my own research through the lens of the agential realist onto-epistemology of theoretical physicist Karen Barad . I briefly present the main points of Barad’s framework before jumping into what I see as being at stake for using maps to propose to city decision-makers and citizens an underground development potential that was otherwise invisible to them before. If maps are indeed far from neutral, then mapping entails important ethical considerations for those who participate in their production. In the case of Deep City, this means making a conscious decision to include and exclude certain information and to analyze the data acquired in a particular way. For the purpose of this colloquium, I focus on the spatial analysis I have adopted for mapping (and measuring) the socio-economic potential of the urban form, which draws on Space Syntax and on the phenomenological underpinnings of its theory. The map that accompanies the presentation illustrates the results of combining this reading of the urban morphology with an analysis of underground resource potential, using data from San Antonio, Texas, in the United States. This communication presents my evolving (and openly debatable) understanding of the map as a discursive practice, and what this means for how we study urban phenomena.