In the last third of the eighteenth century, Naples and Madrid completely transformed their police institutions. A new division of urban space (into twelve quarters in Naples, into eight quarters and sixty-four others in Madrid) was intended to improve the effectiveness of police officers. The urban police is an institution which belongs to its own territory. It requires specific, rationalized and deliberate space districts in order to get a good distribution of the police forces. The creation of new districts and the definition of their limits involved debates among administrations, which led to adjustments and modifications until the beginning of the nineteenth century. This study deals with criteria and requirements which led to the formation of these districts, their successive reforms and the tools that were used to determine their limits. It also deals with their relationship with other urban districts related to various urban administrations, like parishes or municipal wards. Police reform in each of the two cities met with specific limitations which were related to the local institutional sedimentation and its consequences on the territory. Analyzing both cities comparatively throws light on what was at stake in modifying the territorial ordering of urban population.