Tourism flows to large cities have increased drastically in the past few years. The Alfama neighbourhood in Lisbon (Portugal) is facing major changes with respect to land uses, demographic features and social appropriation patterns in public spaces, caused by the intensification of tourism. The consequences of new emerging economic and symbolic values have rapidly given rise to a scenario of touristification and gentrification in the neighbourhood. In order to address such complexities, sustainable urban planning can benefit from real-time data sources that can represent the tourism flows in spatial and temporal perspectives. The research question allows Twitter to be used as an emerging data source and for analysing spatial patterns and content, based on two sample groups: residents and tourists, and their interpretations about the use of space for leisure activities. The research method is based on an analysis of two years of geotagged tweets in the city of Lisbon, differentiating between tourist and resident users, and, in a subsequent step, in the Alfama neighbourhood. The spatial distribution analysis and the content analysis have revealed not only spatio-temporal activity patterns but also emotional responses to new trends in urban tourism uses, consumption and perception of an increasing tourism pressure in Alfama. The results are relevant in the field of tourism and sustainable urban planning.