Index contour lines are characterized by which feature?

• A. Thick brown lines with elevations
• B. Dashed lines
• C. Thick blue lines
• D. Red lines with arrows

Answer: (A)

Index contour lines are the reference lines on a topographic map that show exact elevations. They stand out by being drawn thicker and labeled with their elevation, usually in brown. This makes it easy to read elevation at a glance and to judge how steep the terrain is by comparing the spacing between lines: close spacing means steep terrain, wide spacing means gentler slopes. Between these bold lines, the other contour lines are thinner and unlabeled, so you read the elevation by using the index line as the anchor and estimating the in-between values. The brown color is standard for land elevation contours, while blue indicates water features and dashed lines often represent approximate or supplemental contours, which is why the thick brown labeled line best fits the description.