Products such as those from Mentor Software Inc. let GISes access information in different formats. The uses agencies have for maps range from street to galactic levels. The Air Force is mapping the human body to build better flight suits. Local governments routinely use street and neighborhood maps. Military and civilian agencies use political maps of the world.
Scientific agencies use maps of celestial bodies and special-purpose maps of Earth.
Maps make some handsome images, but it is the data inside that makes them useful. Where you get the data depends on your application of it. As with many maps, you can get data sets, often free, from many sources, including other agencies. The Web is fertile ground for free data sets. But it may make sense to buy data from a private source.