This dissertation considers the emergence of a cartographic public practice in both contemporary art and contemporary cities, attending to the ways in which ephemeral public projects create map-like objects that diverge from official urban projections. Rather than marking a single location, such projects structure networked connections between several sites, transforming undifferentiated urban spaces into legible urban places. Evaluation of this recent cartographic turn entails the triple consideration of placemaking, placemakers, and placemarkers as constructing spatialized identities for different neighborhoods and setting forth wayfinding strategies within these same neighborhoods. Focusing on Manhattan, the dissertation surveys how the borough has served as a source of raw materials from which artists and art institutions constructed new urban models, both against and alongside recent urban redevelopment policies. Three chapter-length case studies constitute this investigation: the public installation, guided tours, and staged Opening Ceremony of REPOhistory's Lower Manhattan Sign Project (1992-1993); the circulating printed image repertoire of the Studio Museum in Harlem's Harlem Postcards (2002-present); and the New Museum's Counter Culture (2004), GET LOST: Artists Map Downtown New York (2007), and new building (2004-2007). By embracing the dual roles of urban archivists preserving marginalized forms of urban visual culture and public artists creating new site-specific and site-responsive projects, each artist collective or organization adopts the mantel of mapmaker. While generating new guides to the city, these mapmakers assert their own presence on the urban landscape as well. In each case, what results is a "processual" map that is responsive to shifting material forms and social dynamics.