  Urbanization has amplified the importance of three-dimensional structures in
urban environments for a wide range of phenomena that are of significant
interest to diverse stakeholders. With the growing availability of 3D urban
data, numerous studies have focused on developing visual analysis techniques
tailored to the unique characteristics of urban environments. However,
incorporating the third dimension into visual analytics introduces additional
challenges in designing effective visual tools to tackle urban data's diverse
complexities. In this paper, we present a survey on visual analytics of 3D
urban data. Our work characterizes published works along three main dimensions
(why, what, and how), considering use cases, analysis tasks, data,
visualizations, and interactions. We provide a fine-grained categorization of
published works from visualization journals and conferences, as well as from a
myriad of urban domains, including urban planning, architecture, and
engineering. By incorporating perspectives from both urban and visualization
experts, we identify literature gaps, motivate visualization researchers to
understand challenges and opportunities, and indicate future research
directions.
