The Nolli map provides an immediate and intuitive understanding of the city’s urban form through the simple yet effective graphic method of rendering solids as dark gray (with hatch marks) and rendering voids as white or light shades of gray to represent vegetation, paving patterns and the like. The city, thus conceived as an enormous mass that has been "carved" away to create "outdoor" rooms is rendered intelligible and vivid through this simple graphic convention.
The idea of solid/void is closely related to the idea of figure/ground. The dark and light patterns of the city reveal the manner in which public space in the city is conceived no less carefully than building. In Rome, public or semi-public space possesses a distinct and identifiable character whether it is a church interior, palace courtyard or public urban space. The Piazza Navona, for example, is easily identified as a "figural" element in the city, with the surrounding buildings acting as a back up field or "ground" into which the element has been placed, or rather, carved away. In contrast, the Modern city reverses this conceptual reading so that building is always seen as active figural object while space is imagined (if at all) as a kind of recessive, formless ether or receptacle that provides the setting for the object. In Rome, solid and void readings have the capacity to be interpreted as either figure or ground.
