We describe the data management principles on which data processing is based in an embedded navigation system. We study this management in the framework of a Web-based navigation and spatial data visualization. We use an Internet-based connection to download the data located on a distant data server and a Web browser interface to process and to visualize them locally. All data are transferred as the result of queries defined on the client side and executed on the data server. The data management on the client side uses a data cache and takes into account the spatial aspect of data. It performs a test for semantic inclusion of results of queries and reuses already available data. We also introduce spatial query restrictions in order to reduce the selected data only to the data set relevant to the actual location of the mobile user. Restriction and semantic caching of queries allows us to reduce the amount of data transferred between a mobile client and a data server.