The paper presents a comparison between aims, theories and practices in city planning and in the use of web-based technologies in urban activities to highlight the different instances of the two macro-domains in conceptualizing city dynamics and elaborating solutions to address urban challenges. The analysis had been structured by considering the three key dimensions constituting the pillars of Urban Informatics: people, city and technology. The analysis had been developed focusing first on the misalignments between current web-based technologies and city planning, then moving to the identification of their convergences. Building on this analysis, the paper outlines three future directions to rethink the integration and future design of web-based technologies in city planning actions as planning support systems to manage the production and use of city data, the orchestration of local activities, and the integration of city plans with distributed urban initiatives.