Open Data Observatories refer to online data platforms that provide free, real-time and historical data. They facilitate collaborative and unified environments for citizens and applications, supplemented with reusable datasets, analysis tools and interactive visualisations. Open Data Observatories collect and integrate various data types from multiple disparate providers. Data types include variables such as weather, traffic and social media, while providers are mainly the interconnected devices, services and individuals in the Internet of Things (IoT). The continually increasing volume and variety of such data require timely integration, management and analysis - yet to be presented in a way that end-users can easily understand. Data that interact in real-time preserve their value and enable a more in-depth understanding of real-world choices. This survey explored Open Data and reviewed twelve data observatories, focusing on their data management approaches. We investigated the observatories aims, designs and data types for some applied domains- namely transport, energy, environment, and social sensing. In what follows, we outlined five research challenges that influence their implementation
