those available through the Google Maps API or through a simple virtual geocaching of "easter eggs" on WikiMapia or similar mash-ups, where permitted; these concepts are virtual worlds making use of mixed reality. Collaborative virtual environments (CVEs) designed for collaborative work in a virtual environment. Massively multiplayer online real-life games (MMORLGs), also called virtual social worlds, where the user can edit and alter their avatar at will, allowing them to play a more dynamic role, or multiple roles. Economy A virtual economy is the emergent property of the interaction between participants in a virtual world. While the designers have a great deal of control over the economy by the encoded mechanics of trade, it is nonetheless the actions of players that define the economic conditions of a virtual world. The economy arises as a result of the choices that players make under the scarcity of real and virtual resources such as time or currency. Participants have a limited time in the virtual world, as in the real world, which they must divide between task such as collecting resources, practicing trade skills, or engaging in less productive fun play. The choices they make in their interaction with the virtual world, along with the mechanics of trade and wealth acquisition, dictate the relative values of items in the economy. The economy in virtual worlds is typically driven by in-game needs such as equipment, food, or trade goods. Virtual economies like that of Second Life, however, are almost entirely player-produced with very little link to in-game needs. While the relevance of virtual world economics to physical world economics has been questioned, it has been shown the users of virtual worlds respond to economic stimuli (such as the law of supply and demand) in the same way that people do in the physical world. In fact, there are often very direct corollaries between physical world economic decisions and virtual world economic decisions, such as the decision by prisoners of war in World War II to adopt cigarettes as currency and the adoption of Stones of Jordan as currency in Diablo II. The value of objects in a virtual economy is usually linked to their usefulness and the difficulty of obtaining them. The investment of real world resources (time, membership fees, etc.) in acquisition of wealth in a virtual economy may contribute to the real world value of virtual objects. This real world value is