While line of sight determines obstructed and unobstructed on a line, a viewshed dictates surrounding areas as visible or non-visible from an observer POV.
Contour lines have constant values on them such as elevation. But it’s also used in meteorology (isopleth), magnetism (isogon) & even drive-time (isochrones)
Topographic profiles are cross-sectional views showing elevation along a line with applications in engineering, hydrology, land use planning and more.
In the mountains, the terrain slopes are in all directions – east, west, north and south-facing. The compass direction that the slope faces is slope aspect.