In the process of modern urban development, cities face various challenges such as climate change, air pollution and poverty, which have negative effects on urban sustainable development and self-regulation. The construction of smart cities can effectively improve the capability of urban management and operation. In this paper, we aim to explore how to use the big data in urban physical, social and cyber spaces to construct smart cities. The concept of digital urban space is proposed to help achieve the construction of smart cities, and city profiling is accordingly presented as a construction method of digital urban spaces and city profile as a product. According to the goals of constructing digital urban spaces, we illustrate the conception and core implementation steps of city profiling, including urban facets modelling and urban facets profiling with smart data. With three application scenarios, we discuss how city profile can be used to meet the factual needs of management, operation and decision-making. City profile can model the cities with urban data and make them become organisms managed and operated by data, so that various information services related to the city can be provided to different users.