We have Comcast, and the Xfinity "hot spot" "extra" service that is open to anyone who is signed on to their Comcast account. ( I could, but do not block this "hotspot" service) As I drive around my neighborhood, (almost entirely Comcast, as we have no other highspeed internet available)... I can see and connect to any one of the Xfinity routers in home where the service has not been blocked.
I leave mine "open", so our kids, friends and visitors can connect without me giving out my own code. Occasionally, cars trucks and sometimes stop in front of our house, and I know they are using my signal. No cost to me, and I trust that they can't hack into my encoded signal.
Where the wifi comes from? I'll defer to more knowledgeable members, but as I understand it, fiber optic cable runs through our area, but connects to terminals that provide the wire feed to our houses. In our Florida community, the fiber optic cable goes to the just outside the entrance and splits to wired connections to the 360 homes.
We pay for 25 mbps, but the 6mbps service is much less expensive. For considerably more ($100+) 100+ mbps service is available.
The only other service available here, is AT&T... DSL with a max of 6mbps, but more commonly 3mbps, or less, which just barely provdes for streaming service such as NetFLix.
Since I live in a CCRC community, most folks are not tech savvy, and don't know how they get their signal... ie., phones, tablets, computers. Not a simple answer... for a relatively clear explanation of the difference between WiFi and Cellular service, try this:
Wi-Fi and Cellular | OSP Magazine
The article also explains how the "hotspot" network is in the process of evolution.
There are many websites that document "hotspot" locations, usually in businesses, but there is no way to locate the home Xfinity shared service except by driving through the area, as shutting down the Xfinity "extra service" is optional, and can be done at any time.
That's my take... from observation, not geeky knowledge.
Will watch to learn more.