This paper presents systematic approaches to create photo-realistic three-dimensional (3D) digital city systems. In the created 3D digital city systems, prismatic and polyhedral building models are constructed from assorted remote sensing and spatial datasets, including topographic maps, aerial and satellite images, airborne and ground-based LIDAR point clouds. Close-ranged digital photographs and video sequences are used to generate facade texture images for photo-realistic texture mapping of the constructed building models. High performance visualization algorithms based on Level of Detail (LOD) processes are also implemented for real-time, interactive exploration and applications. A few applications of the constructed 3D digital cities to urban development evaluation, environmental simulation, hazard mitigation and crime scene reconstruction are presented to demonstrate the usability of the developed 3D digital city system.