Urban Analytics and City Science Advances in urban informatics Background This special issue on "Urban Informatics" in Environment and Planning B: Urban Analytics and City Science is intended to stimulate discussions on recent trends in urban informatics. Initiated and organised by The Hong Kong Polytechnic University (PolyU), the First International Conference on Urban Informatics (ICUI) (2017) was successfully held at PolyU in November 2017. Following this, the second ICUI (2019) was held at PolyU, Hong Kong from 24 to 26 June 2019. Some 180 participants, including world-leading universities such as MIT, Cambridge, ETH, UCL and organisations from over 16 countries/ regions, attended the ICUI 2019. The second ICUI aimed to bring together researchers, engineers, practitioners and educators in urban informatics and related fields to contribute to a stimulating and dynamic exchange of ideas and technologies, as well as contribute to the publication of this special issue. Over the past few years, scientists from all over the world have conducted innovative research in urban informatics, including 3D modelling of complex cities, cartography, remote sensing, LiDAR, InSAR, transportation and land use, housing, and human geography, to name a few. For instance, the first comprehensive book introducing the principles, technologies and applications of Urban Informatics, edited by W.Z. Shi, M. Goodchild, M. Batty, M.P. Kwan and A.S. Zhang (2021a), has been published by Springer. The ICUI 2019 identified six theme topics for the conference: (1) Urban Science and Systems; (2) Urban Sensing; (3) Urban Big Data Infrastructure; (4) Urban Computing; (5) Urban Problems and Possible Solutions; and (6) Smart Cities. The selected papers in this special issue outlined the research advances in urban informatics, which would further promote the research excellence and development of urban informatics to international communities.