Many countries have been implementing plans for smart-city development in recent years. However, how to plan a smart city effectively is still a big issue deserving further exploration. This chapter reviews the use of big data, such as mobile-phone data and transit smart-card data, which can capture spatial–temporal movement of people in a city to support the planning of smart cities. The chapter reviews how big data are captured, pre-processed and analysed. It then discusses how big data can advance our knowledge in the planning of smart cities with three examples: the study of urban structure, jobs–housing balance and low-to-moderate income group spatial distribution relating to housing policy.