Significant advances in public participation geographic information systems technology and online mapping platforms have not translated into enhanced citizen participation in democratic planning processes. This study contributes to addressing this gap by evaluating the engagement of members of an urban community in sustainable neighbourhood planning through argumentation mapping. The study provided an online public discussion forum, together with a neighbourhood map to which the participants could link their discussion contributions. On the basis of participation statistics, contents of contributions, and responses to a survey, we discuss the participants’ technical and engagement experiences. The sixteen registered participants lived within or near the ‘Queen West Triangle’ in downtown Toronto, Canada. They rated themselves as experienced computer users and consequently found the participation in the online discussion forum to be easy. The contributions showed a great degree of interest and knowledge in the issues of sustainable community development. However, while the majority of participants also rated themselves as comfortable with map reading, they found the handling of the online neighbourhood map difficult and did not use the option to link their comments to the map.