How are 911 calls routed to the correct PSAP?

911 calls are routed to the correct Public Safety Answering Point (PSAP) using the Master Street Address Guide (MSAG) for selective routing. The MSAG is a critical database that contains information about street names, address ranges, and corresponding PSAPs as determined by the geographical location of the addresses.

When a 911 call is made, the system identifies the caller’s location through the Automatic Location Identification (ALI) data, which is matched against the MSAG. This ensures that the call is directed to the appropriate PSAP based on where the call is originating. This selective routing process is designed to ensure that emergency services can respond quickly and efficiently.

Geographical regions alone are not a sufficient method for routing as they may not reflect the most accurate or immediate area of the caller. Additionally, there are well-established systems in place for routing — not a random approach — to guarantee that emergencies are handled by the closest and most relevant resources. The absence of a routing system would undermine the entire effectiveness of emergency response, reflecting the importance of a structured and accurate routing method like the use of MSAG.