This paper aims to contribute to the literature on the geography of external relations of cities. Our overall purpose thereby is to tease out some of the basic principles of alternative approaches to the study of the spatiality of urban systems in the context of economic globalization. To this end, we present an empirical analysis of the urban geography of producer service procurement by 118 of the 300 largest companies in Belgium. The main features of this urban geography of service procurement include (i) the dominance of Brussels as a service city ; (ii) the existence of overlapping urban spheres of influence ; and (iii) the presence of transaction links with foreign cities. The results of our analysis also suggest that, in addition to space- and quality-related decision factors, the intra-firm distribution of decision-making power in multinational firms equally influences the spatiality of transaction links. The relevance of these results is discussed in the context of theorizations of urban systems.