39. 글의 흐름으로 보아, 주어진 문장이 들어가기에 가장 적절한 곳을 고르시오.
A round hill rising above a plain, therefore, would appear on the map as a set of concentric circles, the largest at the base and the smallest near the top.
A major challenge for map-makers is the depiction of hills and valleys, slopes and flatlands collectively called the topography. This can be done in various ways. One is to create an image of sunlight and shadow so that wrinkles of the topography are alternately lit and shaded, creating a visual representation of the shape of the land. ( ① ) Another, technically more accurate way is to draw contour lines. ( ② ) A contour line connects all points that lie at the same elevation. ( ③ ) When the contour lines are positioned closely together, the hill’s slope is steep; if they lie farther apart, the slope is gentler. ( ④ ) Contour lines can represent scarps, hollows, and valleys of the local topography. ( ⑤ ) At a glance, they reveal whether the relief in the mapped area is great or small: a “busy” contour map means lots of high relief. [3점]
* concentric: 중심이 같은 ** scarp: 가파른 비탈 *** relief: (토지의) 고저, 기복