In article <4dd16a1b.6050...@googlemail.com>,
Richard Farmbrough <rich...@farmbrough.co.uk> wrote:
> Depends on the ISP, and, moreover, it depends on the granularity of
> information they provide. Most ADSL ISPs seem to enjoy churning IP
> addresses every 24 hours (possibly small hours resets of their exchange
> equipment). Many geo-attempts I've seem simply use ISP's registered
> addresses (hence eveyone lived in Woking, at one point). Smart reading
> of the traceroute will often give almost street level location but I
> doubt many people do that.
I believe "often" here means "for Virgin Media cable users".
The way VM's network is set up means it's easy to locate users to
(roughly) city level, and often better if you can work out the
subdivisions they use within those areas.
For ADSL users, it makes no sense to assign IP addresses or do routing
based on the user's physical location, because all traffic has to go
through BT (or another wholesale provider) in London anyway, and the
route it takes after it gets to BT is not visible in traceroute. So,
when the user connects the ISP just assigns the first available IP with
no regard to location.
It's possible that there is an ADSL ISP that still assigns IPs based on
physical location, but I've never seen one.
I'm fairly certain (and I've said this before) that for this reason
it's impossible to do city-level geolocation of UK users in any useful
way.
Even worse, MaxMind (the service Wikimedia uses) tries to "guess" the
location of ADSL users, and usually fails. For example, when I used
Andrews & Arnold as my ISP, MaxMind decided I lived in Arnold, Notts.
There was no indication that this location was guessed or might be
inaccurate, so it's not even possible to fall back to UK-wide
geolocation for ADSL users.
- river.
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