Traditional planning struggles to acknowledge the fuzzy and complex character of urban voids such as neglected open spaces, wastelands, informal green spaces, terrains vogues, and vacant lots. Those spaces are characterized by versatility, but this is poorly translated into the usual planning tools based on parcel divisions, land use, and administrative boundaries. Urban voids are not created through usual graphic documents such as master plans. How then should they be represented? This contribution explores the link between the urban fabric and urban voids by studying the edges of these spaces graphically. The doctoral research that informs this paper focuses on a specific type of urban void: the seminatural sites of Brussels. This research uses drawings and graphic representations to explore the role of seminatural sites and their potential to contribute to a qualitative densification of the city. The limits of urban voids were subjected to a graphical research method that highlights the intricacies of the urban fabric's parcel organization. To read and understand plans, it is often necessary to clean them up by redrawing them and retaining only the lines that define the principal organization of the space. In this case, the method consists not only in redrawing but also in decomposing and recomposing cadastral plans to provide a new reading of seminatural spaces. These representations erase the relations between plots and instead point to the relations between open spaces and the urban fabric that surrounds them. This approach has proven to be an important tool and a powerful communication lever though with certain limitations, including the difficulty of its reproducibility. This decomposition of cadastral plans was inspired by artists' approaches, such as Armelle Caron, with her "tidy cities" (villes rangées), and Ursus Wehrli, with "the art of clean up."