This presentation discusses the development of smart cities using big sensor data through collaborative efforts. It describes how sensor data from sources like geo-sensors, mobile devices, and social media can be used to understand human activities and urban dynamics. A smart system is needed to integrate this big sensor data, perform processing and mining, and act as a platform for applications. This will help support decisions by residents, visitors and governments. The presentation then discusses a research project that is developing a middleware architecture for spatio-temporal processing of sensor data. It provides an example of Santander, Spain, which extensively uses sensors. The goal of the collaborative smart city approach is to promote data integration and development of smart environments that benefit citizens.