A city metaphor has become a popular method of visualizing properties of program code. This paper provides an overview of research projects that employ this metaphor for a wide range of software engineering tasks. Until now, projects employing the city metaphor have primarily focused on visualizing static and semi-static properties of software repositories, such as understanding how a program's source code structure is changing over time, and who is changing what. This paper compares these existing code cities and suggests likely avenues of future research.