Topographical maps are uniquely useful in SAR because they depict the 3D shape of the earth.  North, South, East and West are depicted conventionally on topos.  Up and down are shown using contour lines.    

Contour lines (the Squiggly lines) connect points of equal ALTITUDE.   For example, a contour line might connect a series of points that are all 420 feet above sea level.    

The contour interval is the distance between two contour lines.  It is usually 20 or 40 feet on the maps we use.    

When looking at a map, closely spaced contours indicate STEEP terrain.  Widely spaced contours indicate GENTLE terrain.