Defining the Boundaries of Urban Built-up Area Based on Taxi Trajectories: a Case Study of Beijing

The urban built-up area is of great significance for urban planning, construction, and management, and is an important index to measure the degree of urbanization. This study reviews the definitions of the urban built-up area in different countries and analyzes its basic characteristics. The rational and advantages of defining the urban built-up area using taxi trajectory data are described. First, we preprocessed these data and used the density-based spatial clustering of applications with noise (DBSCAN) algorithm to cluster the trajectory points. The urban built-up area was defined by the boundaries of each cluster of trajectory points, generated using the Delaunay triangulation method. A parameter decision model was assessed to determine the best-suited parameter for the clustering algorithm. The taxi trajectory data in Beijing were taken as the experimental data, and the urban built-up area generated according to the proposed method shows high consistency with remote sensing images. The results with the proposed method show that the urban built-up area of Beijing comprises a main area and several suburban areas. The main part appears in block form, with some bulges distributed along the city’s main roads. The suburban areas serve as special functional areas of the city and surrounding towns.