ANS:D - by giving spot levels to salient features at close interval.

D is correct because very flat terrains have minimal elevation over large area, hence spacing between contour lines are large, therefore giving spot will at close interval give good representation. Very flat terrains have a minimum little elevation difference over a large area.

Hence spacing between two contour lines is also very large. Therefore giving spot levels at close intervals will give a better representation of very flat terrains. Contour interval means a vertical difference between two consecutive contour lines.

But here, the horizontal distance between 2 contour lines.

Now, here flat terrain means Horizontal Distance between two contour will very high but vertical distance will be very low. Then it will be called as flat terrain. A should be the correct answer because in hilly areas, the contour lines are close together while they are wider apart on flat slopes. The closer the contour lines, the steeper the slope. The wider the contour lines, the flatter the slopes.