Since the early 1960's these maps have been based on the pioneering relief shading of Eduard Imhof.
Imhof employed the concepts of natural vision where colors of nearby objects are brighter than more distant objects. In the case of a map (from an overhead perspective) the higher elevations get the brightest colors, while the lowest elevations are a grayish blue tint. The map is illuminated obliquely from the left side and is enhanced by contour lines and rock drawings.
The online interactive version seamlessly integrates raster information (scanned paper maps) with vectors (geodata) to the extent that it is often unclear which you are seeing. As you zoom out, the map seemlessly changes scale, while retaining its beauty.
here and/or purchase paper maps here.
Note - this is the last of the "Favorite Maps" series for now but I may have additional installments in the future.