There are so many "leaked" trailers that have survived multiple days on YouTube, it's hard to believe this isn't deliberate. Whatever the case, this silent slideshow of SimCity 5 concept art is alleged to be source material for a GDC announcement, and the game will release in 2013.
Earlier this week, seven images published in a German magazine hinted at a sequel, reboot or re-release for the venerable franchise. Speculation has it Electronic Arts will formally announce SimCity's fifth full edition sometime during GDC this week.
Joystiq notes that the lack of a "5" from the SimCity title could mean the series is getting a reboot, as opposed to a sequel. SimCity 4 released in 2003, with seven titles since then being released mainly for mobile devices.