Real ground is not a series of stepped terraces (except in odd places like Sapa). The contours on a map indicate how the land rises and falls in smoothe curves. [Mountainous terrain with cliffs etc is of course different.]
We can distinguish between 'concave' slopes where the distance between contours decreases as we go uphill and convex slopes where the distance between contours increases as we go uphill.
Concave slopes allow uninterrupted LOS for as long as the slope remains concave.
Convex slopes have large areas of dead ground that an observer higher up the hill cannot see. Effectively intervening contours cast a shadow.
The following diagrams illustrate this.
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