What are the three types of contour lines?

• A. Primary, Secondary, Tertiary
• B. Elevation, Depression, Constrained
• C. Index, Intermediate, Supplementary
• D. Index, Major, Minor

Answer: (C)

Contour lines on topographic maps are shown in three kinds to convey elevation and terrain shape clearly. The boldest lines are index contours; they stand out, are labeled with the elevation, and usually appear every few lines to give you quick elevation anchors. Between those, the standard lines are intermediate contours, which fill in the elevations at the regular contour interval to show the detailed shape of the land. In areas where a bit more detail is helpful but the regular grid wouldn’t show it, supplementary contours are added as lighter or dashed lines at elevations between the normal intervals; they help reveal gradual slopes and finer features without cluttering the map.

So, the three types are index contours, intermediate contours, and supplementary contours. The other naming schemes don’t correspond to the common classifications used for contour lines.