Online mapping platforms enable citizens to generate geographic content that can be geoprocessed and displayed in real time as scientific data. Typically, this is implemented through 3-tier architecture including GIS server software and it may be challenging to achieve a comparable level of online mapping features without it. The aim of this study is to implement geoprocessing in a SaaS WebGIS mapping application with the use of a desktop GIS plug-in. The advantages of the adopted approach are scalability as well as complexity reduction in the IT system architecture, which may be critical for small bottom-up citizen science projects. The downloadable and editable toolbox, transfers this solution to any other WebGIS project based on an ArcGIS Online platform. We test our WebGIS approach on a visual pollution case study (Lublin, E. Poland), well-recognized phenomena concerning both citizens and cityscape, and an emerging research topic in international literature. Until now, visual pollution hasn’t been applied to citizen science research, so this paper also introduces a first methodology of integrating WebGIS in visual pollution studies. Our findings have demonstrated that georeferenced web-based polling can be quality-checked, geoprocessed, and interactively visualized with detailed statistics in near real-time without using a GIS server.