Application systems in the earth observation area can be characterised as distributed, platform-inhomogeneous, complex, and cost intensive information systems. In order to manage the complexity and performance requirements set by these application scenarios a number of architectural considerations have to be applied. Among others the most important ones are modularization towards a component architecture and interoperation within this component model. As will be described in this paper, both are mandatory to achieving a high degree of reusability and extensibility at the component level as well as to support the necessary scalability properties. In our paper we refer to the state of the art in earth observation application systems as well as to a prototype system that reflects to a high degree the above mentioned system characteristics.