Chôjô is a research project that investigates the possibilities of collaborative, persistent, location-specific experiences that layer 3D virtual worlds over the physical world. This research has led to a Chôjô game in which the USC campus is the playfield. In the game, players use Personal Digital Assistants (PDAs) coupled with Global Positioning Systems (GPS) to “see” on the PDA screen where they are in the 3D virtual world. With their GPS equipped PDAs, players walk through the USC campus, leaving behind a trail of virtual flora, represented as colorful, blossoming 3D shapes.