Administrators and operators of next generation cities will likely be required to exhibit a good understanding of technical features, data issues, and complex information that, up to few years ago, were quite far from day-today administration tasks. In the smart city era, the increased attention to data harvested from the city fosters a more informed approach to city administration, requiring involved operators to drive, direct, and orient technological processes in the city more effectively. Such an increasing need requires tools and platforms that can easily and effectively be controlled by non-technical people. In this paper, an approach for enabling "easier" composition of real-time data processing pipelines in smart cities is presented, exploiting a visual and block-based design approach, similar to the one adopted in the Scratch programming language for elementary school students. The proposed approach encompasses both a graphical editor and a sound methodology and workflow, to allow city operators to effectively design, develop, test, and deploy their own data processing pipelines. The editor and the workflow are described in the context of a pilot of the ALMANAC European project.