What are the location detecting tecniques for IP adresses?
I know to look at the
$_SERVER['HTTP_ACCEPT_LANGUAGE'] (not accurate but mostly useful to detect location, for example if an IP range's users set French to their browser then it means that this range) belongs to France
and
gethostbyaddr($_SERVER['REMOTE_ADDR']) (to look country code top-level domain)
then may be to whois gethostbyaddr($_SERVER['REMOTE_ADDR'])
sometimes:
$HTTP_USER_AGENT (Firefox's user agent string has language code, not accurate but mostly can be used to detect the location)

But what about cities?