The aim of this paper is to study the implementation of a Web-based public participation geographic information system (PPGIS) with open-source technology and its integration with an online questionnaire. Its theoretical foundations are based on previous work in PPGISs, online surveys, field research, and map-based surveys. The concept of a PPGIS that interlinks interactive GIS maps with an online questionnaire was developed. The concept was implemented with open-source technology and tested in a public participation process designed with the European project SWITCH. The study case was taken from a city district, Wilhelmsburg, in Hamburg, Germany. The combination of the GIS maps combined with the online questionnaire enabled the inhabitants of Wilhelmsburg to draw their answers directly into the online maps. The results of the participation processes were saved directly into the central database. The paper concludes with a critical discussion and directions for further research.