Data warehouses and OLAP systems help to interactively analyze huge volumes of data. Spatial OLAP refers to the integration of spatial data in multidimensional applications at the physical, logical and conceptual level. In order to include spatial information as a result of the decision-making process, we propose to define spatial measures as geographical objects in the multidimensional data model. This raises problems regarding aggregation operations and cube navigation in both semantic and implementation aspects. This paper presents a GeWOlap, a web based, integrated and extensible GIS-OLAP prototype, able to support geographical measures. Our approach is illustrated by its application in a project for the CORILA consortium (Consortium for Coordination of Research Activities concerning the Venice Lagoon System).