Abstract: This paper presents a rigorous method to check the data transformation of GIS, and first proposes the algebra isomorphism or homomorphism to protect the availability of data for sharing in the environment of net work. The data transformation in GIS is a high frequency and trouble work, especially in distributed GIS.It roots in the four kinds of requirements to collecting, inheriting, sharing, and integrating multisource data.The GIS data are managed by normal DBMS and graph DB, and accessed by the commands, interactive tools, API, CGI, SQL, and so on.The space information saved in all kinds of structures is different each other in their semantic methods.When the format of data is changing, we should observe the transfer between two kinds of semantic information in the data, which is the center of the transform.Although many researchers have done many works, the question still exist, even more exacerbating.First, it is difficult to evaluate the change between both semantics.The static transformation is from files to files, and the dynamic one needs to access the source file formats directly.On the other hand, there isn't any standard for the quality of the transformation.Now the authors uses the concept of algebra isomorphism in the transformation to build a way to evaluate.If the transform between the both GIS data is not an algebra isomorphism, then, the semantics between them must vary, and so this transform is not successful.Using the feature of the algebra isomorphism in the GIS format transform is efficient in GIS.It is also a basic method to resolve the same difficulty in distributed GIS.