Digital maps are usually stored in vector format in a database for accessing and retrieving the data using spatial location as the search key. The vector format is a good approach if the user has sufficient hardware and software resources, and if the maps are available in a compatible vector format. The use of map database, however, can be impractical in mobile environment, as the devices may not have enough resources to store the complete map database and the database engine. 

The biggest problem of the vector format is that maps are not always available for the user in vector format. The maps are also stored in various formats and incompatibility between different systems can restricts the use of the maps. In this cases, the raster image format is the only choice. As the maps are often used for viewing purpose only, it is sufficient to provide the user with a raster map. The use of raster map is straightforward: the map is already stored in the form it will be used. The conversion of the maps is also not a big problem. The system does not depend on any database or vector format as digitized raster maps can be easily generated and reproduced from any source format, including paper maps.