Comment by toast0

That only really works if ISP routing is drastically different than it usually is. When I was on DSL at my current house, the IP range available covers basically the whole multi-county metro area; all paths go through the PPPoE concentrator in a single location. You could maybe make a distance estimate from the concentrator, but there's no way to get more information than that.

I think the cable company is a bit more refined, I see cities in traceroutes that don't make sense for the whole metro area to route through, so it's likely that you can determine county, and possibly more specific. But you won't get any useful information from trying to ping outside resources; ISP networks all interconnect at the local internet exchange (or there about), when I had access to a DSL, a cable, and a local fiber ISP all in the same city, pings all went back to the IX. Maybe if you have a lot of presence in an ISP, you can gather a bit more data about users in that ISP, but it won't help you gather data about users on other ISPs.

Disabling pings is nice and all, but if you exchange any traffic, round trip times are pretty easy to gather from that. Delayed ack ads a bit of a challenge, but not much.

Of course, many isps offer geofeeds for their IPs. That's pretty reasonable to use if offered.