On the receiving end, every 911 call here in Lincoln begins like this:
"911, where is your emergency?"
Notice that the first question isn't what is your emergency, but rather where. Location is critical, and believe it or not, it has become more difficult recently, rather than easier. This article by Paul Hammel in the Omaha World Herald provides a detailed description of the problem, but in a nutshell, the demise of the landline and the proliferation of cell phones is the cause.
The technology of 911 is now approaching age 50, and was developed over the decades to function with copper wire telephone switching systems, in order to identify the subscriber and the subscriber's address. The location was fixed: you could pretty much count on the Princess phone being in the same place to which the bill was mailed every month. Today, however, over 70% of the inbound 911 calls come from cell phones, which are not as easy to locate as you might think.
Sure, you can navigate to the nearest frozen yogurt with Google Maps, watch your daughter on Find my Friends, and vector in for the meet-up with Glympse. You would think it would be a simple matter to pass location information along with a 911 call, but it's not the case. Only about 55% of the wireless 911 calls in Lincoln come with what is known as Phase II location information, which locates the phone within a few dozen meters of its presumed location.
Your smartphone gets operating system updates a few times every year, replaced every couple of years, and the carrier is constantly expanding coverage and capabilities. Your 911 system, however, was designed in a different era, and is composed of an immense, expensive network of hardware and software that is not easily upgraded.
It will change, as circuit-switched 911 systems become packet switched NexGen 911 systems, but the change won't be nearly as rapid as the world of consumer electronics, where massive profits drive innovation. So for the time being and into the mid-term future, you best know where you are when the chips are down, so you can pass the most precise information along to the 911 operator. The best information still comes from the caller, not his or her device.