The data is available as spreadsheet/table, maps, for Google Earth, in an animation video and for GIS data download. The data has been retrieved from the UN Population Division publication and web service World Urbanization Prospects, 2007 revision, and georeferenced using a variety of sources.
The database is available for unrestricted download, under the Creative Commons 2.5 attribution license. This gives you the right to reuse and modify the data, as long as Nordpil and the UN Population Division are properly credited. See http://nordpil.com/go/resources/world-database-of-large-cities/
