Correct Answer: Places of equal altitude

Solution : The correct answer is Places of equal altitude.

Contours are the imaginary lines used in cartography to indicate places of equal height or altitude. A contour interval is the difference in elevation between the contour lines. Three types of contour lines are used to show topographic features. They are intermediate, index, and supplementary. Supplementary lines show flat terrain, index lines show elevation above sea level and are the thickest of all lines, while intermediate lines are the most common lines and don't have any number labels.