A well-functioning Emergency Medical Service (EMS) system is a fundamental requirement for saving lives in a Mass Casualty Incident (MCI). While the benefit of strengthening an EMS system is obvious, it is not so evident which components in an EMS system will most contribute to its performance. Using the Emergency Medical Service Simulation model (EMSSim), we test a hypothesis that the social infrastructure and geographic characteristics are key factors in determining the best strategy for the improvement of the EMS system of a particular region. Specifically, we investigate an MCI scenario in three regions metropolitan, urban, and rural environments, and analyze the factors that will effectively enhance the EMS system in each of these regions.