ESNs

The ESN (Emergency Service Number) is a code assigned to each line of the MSAG. It tells the telecommunicator which fire protection, law enforcement and emergency medical service to send to any given address in the county. The ESN is a core element in theEnhanced 9-1-1 system. ESN boundaries are determined by overlaying Fire Service Boundaries, Ambulance Service Boundaries and Law Enforcement Boundaries (usually corporate limits) on the same map. Every polygon on this composite map has it’s own ESN and all roadsegments in that polygon are coded with this ESN in the MSAG. Each polygon is a separate zone. Where boundaries are determined by roads,homes on one side of the road (even numbers) are often coded with a different ESN than the homes on the other side of the road (odd numbers).