In this article we evaluate the viability of using big data produced by smart city systems for creating new official statistics. We assess sixteen sources of urban transportation and environmental big data that are published as open data or were made available to the project for Dublin, Ireland. These data were systematically explored through a process of data checking and wrangling, building tools to display and analyse the data, and evaluating them with respect to 16 measures of their suitability: access, sustainability and reliability, transparency and interpretability, privacy, fidelity, cleanliness, completeness, spatial granularity, temporal granularity, spatial coverage, coherence, metadata availability, changes over time, standardisation, methodological transparency, and relevance. We assessed how the data could be used to produce key performance indicators and potential new official statistics. Our analysis reveals that, at present, a limited set of smart city data is suitable for creating new official statistics, though others could potentially be made suitable with changes to data management. If these new official statistics are to be realised then National Statistical Institutions need to work closely with those organisations generating the data to try and implement a robust set of procedures and standards that will produce consistent, long-term data sets.