You are correct in a general sense but it seems you're stretching the
truth a little bit. Since you only get three octets from GIS, it is
impossible to know "exactly" how many people visit your site. As for the
"from where," you could get a rough idea of location through GeoIP on
three octets, but the result would be generalized. The generalized data
would still be useful, but it would be lacking in resolution and
reliability compared to GeoIP on the full four octet IP address.
The approaching exhaustion of IPv4 in the coming years, and how, in
practice, it is handled could make a real mess of GIS. If your ISP
starts handing out IPv4 addresses in the private address space to
customers and does transparent PNAT, then GIS breaks badly for all
customers of said ISP. In the case of large ISPs, GIS could actually
make things slower.
The part I have no clue about is how GIS works with IPv6? I haven't read
the IETF draft, so I'll just shut up and hope someone more knowledgeable
chimes in here.
> The generalized data would still be useful, but it would be lacking in resolution and reliability compared to GeoIP on the full four octet IP address.
How is that? ARIN doesn't delegate IP address space to users or ISPs in smaller segments than 1024K IP addresses. So it seems that 3 octets is enough to map to a physical location. How does the additional octet give you additional geolocational abilities?
Good question. The answer is in understanding the details. The RIR's
(Regional Internet Registry - ARIN, RIPE, APNIC, ...) do allocate large
blocks as you state, but those large blocks are divided into subnets.
When you realize the subnets have routers and routers often provide
their GPS coordinates, you can see how Geolocation can become more
accurate with more address bits. That's just one of the ways. Another
way would be the subnet assignments often being public and location of
the company/organization with said assignment having a known location.
Still another approach is the looking up locations based on AS/ASN. And
yet another is GPS reporting (think mobile android/ios). There are
probably other ways that I don't know. The important part to realize is
how all of the various methods are both employed and combined to build
out geolocation databases. Geolocation by IP is far from perfect, but
often it can be surprisingly accurate.
Even with the full IP address, GeoIP won't necessarily tell you much. My location has been reported as York, Cambridge, City of London and the Netherlands, all of which are 100+ miles away from my actual location.
The approaching exhaustion of IPv4 in the coming years, and how, in practice, it is handled could make a real mess of GIS. If your ISP starts handing out IPv4 addresses in the private address space to customers and does transparent PNAT, then GIS breaks badly for all customers of said ISP. In the case of large ISPs, GIS could actually make things slower.
The part I have no clue about is how GIS works with IPv6? I haven't read the IETF draft, so I'll just shut up and hope someone more knowledgeable chimes in here.