This paper presents a 3D visualization approach which gravitates around the city metaphor, i.e., an object-oriented software system is represented as a city that can be traversed and interacted with: the goal is to give the viewer a sense of locality to ease program comprehension.The key point in conceiving a realistic software city is to map the information about the source code in meaningful ways in order to take the approach beyond beautiful pictures.We investigated several concepts that contribute to the urban feeling, such as appropriate layouts, topology, and facilities to ease navigation and interaction.We experimented our approach on a number of systems, and present our findings.

Assessing the quality of software design is difficult, as "design" is expressed through guidelines and heuristics, not rigorous rules. One successful approach to assess design quality is based on detection strategies, which are metrics-based composed logical conditions, by which design fragments with specific properties are detected in the source code. Such detection strategies, when executed on large software systems usually return large sets of artifacts, which potentially exhibit one or more "design disharmonies", which are then inspected manually, a cumbersome activity.In this article we present disharmony maps, a visualization-based approach to locate such flawed software artifacts in large systems. We display the whole system using a 3D visualization technique based on a city metaphor. We enrich such visualizations with the results returned by a number of detection strategies, and thus render both the static structure and the design problems that affect a subject system. We evaluate our approach on a number of open-source Java systems and report on our findings.

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The comprehensive understanding of a large software system is a daunting task because of the sheer size and complexity that such systems exhibit. In this context software visualization is a widely used approach, since well-conceived visual representations allow one to spot patterns. The large majority of visualizations use 2D representations, because they are easier to construct, navigate, and interact with. 3D representations usually exploit the 3rd dimension as an additional means to encode quantitative values, which is dismissed by many as a too small benefit in the light of the added complexity in terms of navigation and interaction.We argue that a well-constructed, interactive, and easily navigable 3D visualization can greatly help in program comprehension tasks by supporting habitability. Habitability transmits to a developer the notion that a software system is a physical space with strong orientation points. This can give developers the feeling of being "at home" in a system. We propose a 3D visualization of software systems hinging on the city metaphor. It is useful for program comprehension because it leads to clarity about the overall structure of a system. We apply our visualization technique on two large systems and discuss its benefits and drawbacks.

Code duplication is a common problem, and a wellknown sign of bad design. As