Recent years have witnessed the rapid development and wide adoption of immersive head-mounted devices, such as HTC VIVE, Oculus Rift, and Microsoft HoloLens. These immersive devices have the potential to significantly extend the methodology of urban visual analytics by providing critical 3D context information and creating a sense of presence. In this paper, we propose a theoretical model to characterize the visualizations in immersive urban analytics. Furthermore, based on our comprehensive and concise model, we contribute a typology of combination methods of 2D and 3D visualizations that distinguishes between  linked views, embedded views, and   mixed views. We also propose a supporting guideline to assist users in selecting a proper view under certain circumstances by considering   visual geometry >  and   spatial distribution   of the 2D and 3D visualizations. Finally, based on existing work, possible future research opportunities are explored and discussed.