Your info won't be shared for other purposes, Apple said, and only the relevant 911 center can see your location.

The company has already been sharing a rough estimate of your location using triangulation from cell sites, GPS and WiFi hotspots. However, that approach (Hybridized Emergency Location) tends to have a considerably larger margin of error, especially in dense cities that might interfere with GPS. The increased accuracy in iOS 12's implementation could ensure that emergency crews arrive exactly where you need them, even when you aren't in a position to give them a street address.

The finished version of iOS 12 is due to arrive in the fall, most likely in September.