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Advanced sensing technologies and computing infrastructures have produced a variety of trajectory data of moving objects in urban spaces. One type of this data is taxi trajectory data. It records real-time moving paths sampled as a series of positions associated with vehicle attributes over urban road networks. Such data is big, spatial, temporal, unstructured and it contains abundant knowledge about a city and its citizens. Exploratory visualization systems are needed to study taxi trajectories with efficient user interaction and instant visual feedback. The extracted information can be utilized in many important and practical applications to optimize urban planning, improve human life quality and environment. As the primary novelty contribution, this thesis presents a set of visual analytics solutions with different approaches to interacting with massive taxi trajectory data to allow analysts to look at the data from different perspectives and complete different analytical tasks. Our approaches focus on how people directly interact with the data store, query and visualize the results and support practitioners, researchers, and decision-makers to advance transportation and urban studies in the new era of the smart city.First, we present SemanticTraj, a new method for managing and visualizing taxi trajectory data in an intuitive, semantic rich, and efficient means. In particular, taxi trajectories are converted into taxi documents through a textualization transformation process. This process maps global positioning system (GPS) points into a series of street/POI names and pickup/drop-off locations. It also converts vehicle speeds into user-defined descriptive terms. Then, a corpus of taxi documents is formed and indexed to enable flexible semantic queries over a text search engine. Second, we present a visual analytics system, named as QuteVis, which facilitates domain users to query and examine traffic patterns from large-scale traffic data in an urban transport database. QuteVis supports a different type of data query and analytical tasks. It helps users discover those specific times and days in history that have similar traffic patterns as they speculate on multiple, spatially-diverse city locations.Third, we present a web-based software, named TrajAnalytics, for the visual analytics of urban trajectory datasets. It allows users to interactively manage, analyze, and visualize the massive taxi trajectories over urban spaces. The software offers data pre-processing and management capability and enables various visual queries through a web interface. Finally, a set of visual exploration tools have been implemented to be utilized in the systems above for visual exploration of trajectory data. These visual exploration tools are considered as an effective approach to providing material for human’s perception and plays a vital role in analyzing and visualizing trajectory data.