Geographical Information Systems (GIS) for governmental applications are beginning to be applied on a dual-census or multi-census basis. A dual census GIS is one that references the data of two censuses in an integrated way. Nearly every nation worldwide has a census that constitutes its primary repository of spatially referenced social and economic data. However, censuses vary a lot in their data quality, attribute definitions, and spatial design. This paper has the primary goal to examine to what extent a dual census GIS corresponds to a data warehouse. The paper first presents a contemporary design for a dual census GIS, followed by an example. Then it reviews the key features of a data warehouse and examines feature by feature whether or not a dual census GIS corresponds to a data warehouse. The paper concludes that a dual census GIS mostly corresponds to a data warehouse. It succeeds on features of combining data from multiple sources, but falls short on multi-dimensionality. A dual census GIS emphasizes calculation and modeling to a greater extent than most data warehouses. In this respect, the dual census GIS meets the OLAP criteria, and in particular that of data manipulation. The paper points out that the real advantage of incorporating data warehousing may be to combine it into a spatial decision support system, in order to provide decision support in a bi-national or multi-national context.