Tracking urban geo-topics based on dynamic topic model

Abstract

Modern cities are facing critical environmental and social problems that are difficult to solve using conventional planning approaches due to the cities’ magnitude and complexity. Recent developments in sensing technologies and urban computing, however, integrate new data resources and technologies to tackle these challenges. Popular social networking platforms such as Twitter provide new data sources on important events (e.g., cultural activities, political campaigns, accidents, crises) providing rich knowledge about urban systems and human dynamics. This research is intended to develop a method for effectively monitoring important information during such events and helping with planning and policymaking. We use semantically similar and geographically close geo-topics to represent important local events. This research proposes a data-driven system for detecting and tracking the semantic, spatial, and temporal dynamics of these geo-topics, specifically designed for geo-tagged tweets. The system consists of data preprocessing, geo-topic generation, and geo-topic tracking modules. The preprocessing module can remove robotic and semantically trivial texts. In the geo-topic generation module, we use spatial factors to measure the spatial impacts of geo-tagged tweets by applying an exponential decay function to the pairwise distances between tweets. We then improve the dynamic topic model (DTM) by embedding the spatial factors to enable the generation of geo-topics in semantic, spatial, and temporal dimensions simultaneously. The geo-topic tracking module monitors semantic change by detecting changes in certain keywords’ probabilities and the volumes of tweets belonging to different geo-topics. This module also uses radius of gyration and trajectory-pattern mining to track and analyze the movement patterns of geo-topics. We employed the tracking system in three disaster cases in different U.S. cities to track small-scale emergencies and crises. These implementations demonstrated the effectiveness of the system for identifying and tracking geo-topics at fine temporal and geographic scales. The system also has strong potential in creating planning-related analyses for policy makers, improving the situational awareness of the general public, and serving as a basis for urban information systems that contribute to smart, agile, and resilient city developments.