Understanding, simulating, and forecasting the future of cities in the virtual world are necessary for controlling and analyzing the effect of virtual cities on the real world. Cities, where the global population is gathering and providing a physical environment for citizens, are becoming the locus of virtual, networked-based economic, political, and cultural activities. Thus, digital cities will represent a new manifestation of this phenomenon. Moreover, virtual reality systems give experts visual access to digital information about this environment through initiatives to digitally model and simulate the real environment, users, and services. Virtual models can be used to democratize planning, evaluate many future scenarios, understand how the built environment operates, and train emergency response, maintenance, and operations employees across scales, from buildings and neighborhoods to infrastructure and cities.