When you call 911, the address associated with your phone number is used to direct the call to the correct local emergency response units, known as Public Safety Access Points (PSAPs). The PSAP, in turn, uses that address to direct the emergency response units to your location.
To ensure rapid response times, 911 addresses are standardized so that they are accurate and unambiguous for the emergency response units. The PSAPs are responsible for standardizing all addresses in their jurisdiction. That record of standardized addresses is known as the MSAG (Master Street Address Guide).
Warning
If there is a power or internet outage, your phone may not be able to place a 911 call.