In tandem with the rapid globalisation of science, spatial scientometrics has become an important research sub-field in scientometric studies. Recently, numerous spatial scientometric contributions have focused on the examination of cities' scientific output by using various scientometric indicators. In this paper, I analyse cities' scientific output worldwide in terms of the number of journal articles indexed by the Scopus database, in the period from 1986 to 2015. Furthermore, I examine which countries are the most important collaborators of cities. Finally, I identify the most productive disciplines in each city. I use GPS Visualizer to illustrate the scientometric data of nearly 2,200 cities on maps. Results show that cities with the highest scientific output are mostly located in developed countries and China. Between 1986 and 2015, the greatest number of scientific articles were created in Beijing. The international hegemony of the United States in science has been described by many studies, and is also reinforced by the fact that the United States is the most important collaborator to more than 75 percent of all cities. Medicine is the most productive discipline in two-thirds of cities. Furthermore, cities having the highest scientific output in specific disciplines show well-defined geographical patterns.