Spatial OLAP (SOLAP) integrates spatial data into OLAP and Data warehouse systems to exploit analysis capabilities associated to geographic information. SOLAP extends OLAP operators to navigate into spatial dimensions, and to cut the spatial data warehouse using spatial predicates. Integration of several heterogeneous spatial data warehouses is very useful for decision-makers since they can navigate into multiple data sources. In this paper, exploiting the continuous dimension of spatial data, we propose a new operator to merge spatial data warehouses without conformed spatial dimensions. This operator is based on the spatial analysis transformation called Overlay. We show its implementation in the Web-based SOLAP System GeWOlap.