This paper presents a new navigation system built upon our client-server framework named Magellan. With this system one can navigate through a city model represented with procedural models transmitted to clients over a low bandwidth network. The geometry of these models is generated on the fly and in real time at the client side. The navigation system relies on different kinds of preprocessing such as space subdivision, visibility computation as well as a method for computing some parameters used to efficiently select the appropriate level of detail of objects. These two last kinds of preprocessing are automatically performed by the graphics hardware.