Index contour lines on a map are typically what, compared to other contours?

Index contour lines on a map are typically what, compared to other contours?

• A. Labeled with elevation values
• B. Unlabeled and dashed
• C. Only drawn along water features
• D. Always the outer boundary of the map

Answer: (A)

Index contour lines provide a quick read of elevation on a topographic map. They are drawn bolder and carry the elevation value at that line, so you can know the altitude without counting many lines. This labeling distinguishes them from the regular contours, which are lighter and usually unlabeled and simply indicate the same elevation at the standard spacing. They are not restricted to water features, nor do they form the map boundary; the map boundary is indicated by its own border.

Index contour lines provide a quick read of elevation on a topographic map. They are drawn bolder and carry the elevation value at that line, so you can know the altitude without counting many lines. This labeling distinguishes them from the regular contours, which are lighter and usually unlabeled and simply indicate the same elevation at the standard spacing. They are not restricted to water features, nor do they form the map boundary; the map boundary is indicated by its own border.