Raster maps

Rasters maps are digital maps on the basis of individual pixels. Since each point must be represented on the map with a pixel and the colour, such maps require very much memory on the hard disk. Example for  formats are GEOTIFF or BSB. There is to represent another multiplicity of further formats about maps however.

Why Can't I buy good quality Topographical MAPS of the rest of the world CHEAPLY like I can for the USA?

Bill Straka tells  why not. Source ( http://joe.mehaffey.com/topoworld.htm)

The United States is fairly unique among countries of the world in making detailed topographic and other mapping information freely available for distribution and reproduction. Many other countries do not even have detailed topographic information available. Some of those that do have place severe restrictions on its distribution and reproduction for military security reasons. The countries that were part of the former Soviet Union are one example, along with China, Iraq, and others. India places severe restrictions on maps of certain areas, such as the disputed border regions with Pakistan and China. Most of the remaining countries that do have reasonable mapping data available charge a high licensing fee for reproduction. Canada is one of these. Switzerland is another, even charging very high prices for government-supplied map data on CDROMs.

The land surface of the Earth is over 300 million square miles. Mapping to the same accuracy (1/50 inch on the printed map) as the USGS 7.5 minute topographic maps on a raster scan would require something like 1.3 terapixels (that's 1.3 trillion pixels). You probably want finer resolution, perhaps 600 dots per inch, which boosts the number to 190 terapixels, each of which has associated altitude information and thematic information (vegetation cover, highway type, things like that). Numbers like that show what a huge job it will continue to be to produce detailed maps of the whole world. Maybe you can get away with an altitude grid that is a coarse as the finer parts of the USGS DEM grid (Digital Elevation Model). But this will perhaps give you an appreciation of the accomplishment of those who surveyed just the 48 contiguous states on foot and by hand, only a few million square miles out of the Earth's land surface. There are still parts of the US (Alaska, in particular) that are incompletely mapped to the 1:24,000 scale, and large parts of the world that are mapped only to the 1:500,000 scale, and even areas that remain completely unmapped except for satellite photographs and crude sketches.