Urban complexity is an important aspect and objective attribute of urban sustainable development. For the study of urban complexity, we prefer to use simple methods and models to understand and explain various trends and possibilities of urban development, and to be able to fully recognize various factors in the city and their laws of interaction. With the rapid development of big data, Internet and cloud computing technology, the research of urban complexity has gone through the process from qualitative to quantitative, and from static to dynamic studies, and involving from one single discipline to multidiscipline. The research field of urban complexity has also been extended to transportation, urban planning, computer science, spatial science, and other fields. The science of complexity has become pivotal to urban studies. However, understanding urban complexity from spatio-temporal perspectives is still a largely unexplored area.

The cornerstone of urban complexity research is to define and characterize urban ontology, which is essential to understand spatial-temporal relationships of the geographical objects (phenomena) in urban complex systems. How to represent the spatial-temporal relationships, how to estimate the evolution of geographical objects (phenomena) in urban complex system and how to make sense of geographical objects within the ecosystem of an urban space are challenging problems to researchers in the spatial science.

This Special Issue calls for papers to solve these problems not only in the spatial science, but also in other disciplines. We encourage authors to submit original research and review articles that will focus on developing new methodologies and theories in urban complexity

Potential topics include but are not limited to the following:

• Analysis of scale problems in urban complexity research;
• The impact of technological progress on urban complexity research and its response;
• Advanced and innovative collection and processing programs of big data for urban complexity analysis;
• Theories, methods and applications related to urban traffic complexity research;
• Spatial statistical analysis model for urban complexity research;
• Application of artificial intelligence (deep learning, etc.) technology in urban complexity research;
• Research on urban complexity in the aspects of urban health, livable construction and so on;
• New technology and methods for the research of urban climate and local climate zones;
• Big data processing methods for urban complexity research;
• Visualization techniques for urban complexity research;
• The complexity and resilience mechanism of urban infrastructure networks;
• Urban spatial structure and its complexity from the perspective flow space;
• Complexity measurement of urban morphology and design;
• Sustainable and healthy urban system complexity;
• Complex network analysis of tourism