The MONDIAL database has been compiled from geographical Web data sources listed below:
* CIA World Factbook,
* a predecessor of Global Statistics which has been collected by Johan van der Heijden.
* additional textual sources for coordinates,
* the International Atlas by Kümmerly & Frey, Rand McNally, and Westermann,
* and some geographical data of the Karlsruhe TERRA database
"So URNs and URLs are often complementary; for example, you might discuss an RFC using both concepts: "you can find urn:ietf:rfc:3187 (URN) over at http://tools.ietf.org/html/rfc3187.html (URL)."