Urban information visualization is an essential tool for decision process in urban planning. Nowadays, more and more urban visualizations incorporate virtual 3D city scenes to better convey spatial and morphological information. On the other hand, the development of consumer grade VR devices as Head Mounted Displays (HMD) enable to visualize urban information with a greater degree of immersion. These new ways to render and display 3D city models may have a significant impact on the perception of urban morphology and, consequently, on the interpretation of the urban visualization. In this paper, we present a subjective experiment to evaluate the impact of visual immersion - field of view, stereoscopy and allocentric or egocentric representations - on the perception of urban morphology and density in 3D city models. Obtained results can be useful to improve urban visualization, but also to better understand perception, user behavior and navigation in 3D virtual environments.