Software visualization tools can facilitate program comprehension by providing visual metaphors, or abstractions that reduce the amount of textual data that needs to be processed mentally. One way they do this is by enabling developers to build an internal representation of the visualized software and its architecture. However, as the amount of displayed data in the visualization increases, the visualization itself can become more difficult to comprehend. The ability to display small and large amounts of data in visualizations is called visual scalability. In this paper, we present two approaches to address the challenge of visual scalability in 3D software cities. First, we present an approach to semantic zoom, in which the graphical representation of the software landscape changes based on the virtual camera's distance from visual objects. Second, we augment the visualization with a miniature two-dimensional top-view projection called mini-map. We demonstrate our approach using an open-source implementation in our software visualization tool ExplorViz. ExplorViz is web-based and uses the 3D city metaphor, focusing on live trace visualization. We evaluated our approaches in two separate user studies. The results indicate that semantic zoom and the mini-map are both useful additions. User feedback indicates that semantic zoom and mini-maps are especially useful for large software landscapes and collaborative software exploration. The studies indicate a good usability of our implemented approaches. However, some shortcomings in our implementations have also been discovered, to be addressed in future work.