The Office of Homeland Security and the Centers for Disease Control and Prevention have jointly mandated that cities and localities develop plans for establishing emergency command centers in multiple locations to dispense vaccines and antibiotics and provide security and police coordination in the event of major emergency events, such as terrorist attacks, bioterrorism, and natural pandemics. These command centers must be located such that one is within 15 minutes of every person in the general population. For cities with large populations and geographic areas, this could result in a large number of centers and create logistical problems in setting them up quickly and staffing them. As such, cities would like to create the minimum number of command centers possible. In order to determine where it should locate its command centers, a city has divided its geographic area into four quadrants—northeast, northwest, southeast, and southwest. Within each quadrant, it has established four sectors with potential sites for command centers—A, B, C, and D—usually where there is a sufficient facility capable of housing a center and not necessarily centrally located. The potential command center site in a sector is always within 15 minutes of the population in the other three sectors in the quadrant and also within 15 minutes of the population in some sectors in adjacent quadrants, as shown in the following table:

                            

Determine the location of the minimum number of command centers for the city.