—Development of smart city services is presently hindered because the data is too heterogeneous, despite the increasing availability of data in open data initiatives. We determined metadata fields and semantics for our proposed model after a survey of other event models, and after its trial implementation in actual applications. Our event metadata model is unique among event models in being extensible as needed. We illustrate our model by showing it with different data types, and we validate it using real-world data in a prototype smart cities service for pedestrian safety. Wide adoption of our event metadata model has the potential to broaden the number and scope of smart city services.