This paper proposes a geospatial data visualization system supporting validation of GML documents. GIS systems manage and use both of spatial and non-spatial data. Currently, most GIS systems represent spatial data in GML (Geography Markup Language) developed by OGC. GML is a language for representation and sharing of spatial information, and until now many systems have been developed in GML. GML does not support expression of non-spatial data, i.e., relational information of spatial objects, and thus most systems extend GML to describe non-spatial information. However, it causes an issue that the systems only accepting standard GML documents cannot process the extended documents. In this paper, we propose a new GIS data visualization system to resolve the aforementioned Issue. Our proposed system allows the representation of both types of data supporting independency of spatial data and non-spatial data. It enhances interoperability with other relevant systems. Therefore, we can develop a rich and high Quality geospatial information services.