There are two sources of IP-address data

• When people are good enough to identify their city, it is stored in the DB and associated with the /24 they are currently using. This is obviously the best info. source.
• There are (currently 10) robots on the server, tracerouting to IP addresses within /24's that we haven't yet identified. There are then several hundred regular-expression rules (from sarangworld) which match parts of the names detected to countries/cities..

The tracerouting has provided the most data so far (it's just constantly churning away in the background), but I think most of the major trunks from my server location have been identified, so I expect it to tail off.

The map data all comes from the NOAA, and uses their 30 arc-second/pixel data for the highest-resolution maps. It's not clear whether I ought to cite them or not, but I'll do so anyway, just for being such nice people and making public the data :-)

GLOBE Task Team and others (Hastings, David A., Paula K. Dunbar, Gerald M. Elphingstone, Mark Bootz, Hiroshi Murakami, Hiroshi Maruyama, Hiroshi Masaharu, Peter Holland, John Payne, Nevin A. Bryant, Thomas L. Logan, J.-P. Muller, Gunter Schreier, and John S. MacDonald), eds., 1999. The Global Land One-kilometer Base Elevation (GLOBE) Digital Elevation Model, Version 1.0. National Oceanic and Atmospheric Administration, National Geophysical Data Center, 325 Broadway, Boulder, Colorado 80303, U.S.A. Digital data base on the World Wide Web (URL: http://www.ngdc.noaa.gov/seg/topo/globe.shtml) and CD-ROMs.

The city data comes from various places around the 'net as well as from a major data donation. Some US data is from the US census data, other countries from other sources on the internet.

The database is organised as a 256 by 256 by 256 cube which correspond to the top-3 bytes of the IP address space (commonly called a /24 since it takes 24 bits to hold 3 bytes). Each point in the cube can hold a city. There are currently some 7 million or so points to map... it'll take a while [grin].