From Brickipedia, the LEGO Wiki
World City is a subtheme of Town that was introduced in 2003. It featured several sets that involved police, firefighters, Coast Guards, and Trains.
After the discontinuation of City Center in 2001 there were no new releases of town life related LEGO System sets until the introduction of World City in 2003 (although there have been some rereleases in the meantime, as well as continued releases of the Trains theme). World City's last new sets were released in 2004. The theme was succeeded by City which was introduced in 2005.