Garmin, Magellan, and Lowrance have all released vector maps for their respective units. None of these are interchangeable and no other software can be used to upload map data to these units, except that you can modify the maps by adding vectors to the maps in the Lowrance units using third party programs. There are other, more expensive, systems that can support the uploading of your own vector maps. For example, Trimble makes a professional model that can be used to generate maps in the first place and can load and display these maps. Unfortunately you must always supply your own source of maps with this unit.
Vector maps can provide a lot of detailed road data but can be hard to prune to serve as road maps.
Generally they work well for large areas only if you can remove all of the street level detail from the database. Bitmap maps can provide coverage for large areas with a minimum of space but will start to take significant space if you expect to be able to vary the detail by zooming. Both map types have their purpose as witnessed by the latest Delorme mapping product, Solus Pro, that supports both types in the same program.