We report our experience in mapping SEF — a data exchange standard for topographic map in Taiwan — to GML. Often there are two goals in such a schematic mapping: Preservation and improvement. That is, the new vocabulary must be used in a way that it losslessly carries over all information that is expressible in the old format, but at the same time opens up opportunities for new functionalities. We discuss in this paper the requirements and design choices we face in mapping the SEF data format to a GML application schema, as well as various visualization issues in a GML-to-SVG mapping. We have built the necessary SEF-to-GML and GML-to-SVG conversion tools, and have used them to process and visualize existing topographic data. Real-world examples are shown in this paper.