This paper analyzes the development of an inventory of vacant buildings and land in Trenton, New Jersey that resulted from a research partnership between the Rutgers University Center for Urban Environmental Sustainability; Isles, Inc. a Trenton-based non-governmental organization; and the City of Trenton. Participatory research design between university and NGO staff led to a smartphone GIS survey tool that functioned through web and desktop GIS. University students and community residents collected data through a smartphone GIS application and visually inspected almost every property within the city’s boundaries. Although many vacant land inventories have successfully used secondary data, this project required fieldwork to identify vacant properties because data were unavailable through secondary data. The survey was developed collaboratively with the NGO for their use and modification of it in future work, and to understand locally-specific visual markers of vacancy. The data informed the City of Trenton’s vacant property management policy, and served as a foundation for a variety of Isles’ community development programs. While smartphone applications may improve NGO access to GIS, the need for web and desktop GIS to complete data collection and analysis requires expertise and time that pose additional challenges.