With the property of XML, RDFs, ontology and logic, Semantic Web provides intelligent services on the Web. Taking the advantages of Semantic Web, semantic WebGIS can realize semantic interoperability and integration of GIS on the Web. The key basis of semantic WebGIS is its domain ontology. As an information exchange standard, XML is an important method of implementing semantic WebGIS. The combination of domain ontology and XML can take the strengths of both to resolve the semantic interoperability problem. In this paper two examples are given to illustrate how this method works in solving queries on semantic heterogeneous information. An architecture based on ontology server mediator and wrapper is presented as a system solution.