The smart city is based on digital data that can contribute to a better understanding and efficient management of urban processes. These data, which are produced by devices and citizens through online and social media activities, are usually managed and exploited by big tech companies. We claim that digital sustainability is tightly connected to environmental sustainability. Citizens have lost control over data-driven processes that are happening on a global arena. However, communities, through their online communication, can contribute to an alternative narrative and the creation of public spaces that constitute the premise to build more sustainable cities. In this paper, a social media analysis of the Twitter communication of two grassroots communities (i.e., creative skilled migrants living in Amsterdam and Dutch elderly) is carried out. It is based on a language analysis of geo-tagged data, combined with a social network analysis that show the contribution of these two groups to the smart city debate. Their different voices can give rise to more sustainable cities in which social equity and environmental protection become priority themes. These two communities exploit the available Twitter space, as a contact zone. Even though there might not be a clear political purpose in their narrative, the interaction between the local and global level of communication (mediated by social networks) gives rise to a space that stimulates participation, and has the potential to contribute to a more sustainable urban future
