A smart city is more than its mere technological components. From a legal standpoint, smartness means a civic-enabling regulatory environment, access to technological resources, and openness to the political decision-making process. No doubt, the core asset of this socio-technical revolution is the data generated within the urban contest. However, national and EU law does not provide a specific regulation for using this data. Indeed, the next EU data strategy, with the open data and non-personal data legislation and the forthcoming Data Act, aims to promote a more profitable use of urban and local big data. Nonetheless, at present, this latter still misses a consistent approach to this issue. A thorough understanding of the smart city requires, first of all, the reconceptualization of big data in terms of urban data. Existing definitions and studies about this topic converge on the metropolises of East Asia and, sometimes, the USA. Instead, we approach the issues experienced in medium-size cities, focusing on the main Italian ones. Especially in this specific urban environment, data can help provide better services, automatize administrations, and further democratization only if they are understood holistically - as urban data. Cities, moreover, are a comprehensive source of data themselves, both collected from citizens and urban things. Among the various types of data that can be gathered, surveillance recordings play a crucial role. On the one hand, video surveillance is essential for many purposes, such as protecting public property, monitoring traffic, controlling high-security risk areas, and preventing crime and vandalism. From another standpoint, these systems can be invasive towards citizens' rights and freedoms: in this regard, urban data collected from video surveillance systems may be shared with public administrations or other interested entities, only afterward they have been anonymized. Even this process needs to be aligned with the transparency and participation values that inform the city's democracy. Thus, the anonymization process must be fully compliant with data protection legislation, looking for the most appropriate legal basis and assessing all the possible sources of risks to the rights and freedoms of people (DPIA). Urban data, indeed, is a matter of local democracy. The availability of data and the economy of platforms can significantly transform a city's services and geography as well as citizens' lifestyles. However, the participation of citizens to express their views on both the use of urban data for public policy and the regulation of the digital economy is still a challenge. The paper aims to analyze the projects of some Italian cities - including Milan, Rome, and Turin - which have tried to introduce participatory urban data management tools and to highlight the possible challenges of a democratic management of service platforms and data transfer for social and economic development
