How to build a IP geolocation database from scratch?
a long time ago i build a project like that
but instead of relying on whois. i did a traceroute to every ipv4 address avaliable.
several router hops, have a reverse dns that uses some names that include city codes, (like airport codes ).
most providers have a single hop for a city. so its easy to correlate the latest router hop to a city.