Effective management of infrastructure development in large urban agglomerations requires diagnosing interdependencies occurring in the process of its development. This specific interdependence, links between various types of infrastructure, not only favours the development of agglomerations, but also generates threats with unprecedented consequences for public safety and order. Damage to one element of urban infrastructure may adversely affect another element, which in turn may result not only in threats to the safety of people living in the agglomeration, but also in threats to the state. Therefore, the issue of making the key infrastructure of an urban agglomeration more resilient should be considered in the context of system connections of state infrastructure elements, as well as the criticality of its individual elements, nodes and key points. The aim of this article is to present the importance of the diagnosis of connections and dependencies between elements of the city (state) infrastructure in the process of determining the essential service and, consequently, the proper immunization of critical infrastructure. The main research method used in the course of the research was the critical analysis of literature, materials and procedures. The publications of both Polish and foreign researchers on the links and dependencies of the state infrastructure and the determination of key services were analysed. The conducted analysis indicates the need to conduct research in Poland on diagnosing dependencies in the developing infrastructure. This need results from the dynamic nature of threats and the emergence of new technologies that support the development of modern agglomerations and make the state more sensitive to other, so far undiagnosed threats