||With the rapid development of 3D modeling and rendering technologies, it is now possible to model a whole city and put it online, which opens doors to many applications, especially for tourists to virtually explore a city and plan their tours. In this thesis, we propose two visualization techniques for 3D urban environments. We first present a 3D city map generation system that can turn 3D models of a city into a more informative layout in which the structure of the city, major roads, and landmark buildings will be better revealed over the context of a realistic 3D environment. The system integrates principles having been used by artists for making 3D maps for centuries and automates the entire process with little user guidance. We then propose a novel interaction technique, called focus+context route zooming, which allows users to zoom into a route and its associated landmarks in a 3D urban environment from a 45-degree bird's-eye view. Through the creative utilization of the empty space in an urban environment, our technique can informatively reveal the focus region and minimize distortions to the context buildings. Both techniques can be conveniently integrated into Google Earth and Virtual Earth to help users better explore a city and plan their tours. They can also be used in other applications such as information overlay to a virtual city.