Informational cities are prototypical cities of the knowledge society. According to Castells, in those cities space of flows (flows of money, power and information) tend to override spaces of place. Infrastructures of information and communication technology (ICT) and cognitive infrastructures have a high impact on urban development and economic growth. This conceptual article frames indicators which are able to mark the degree of “informativeness” of a city. The aim of our article is to provide a basis for further informational city research and to demonstrate a theoretical framework with the help of a case study (with the example of Singapore).