Index contour lines are defined as which of the following?

Index contour lines are defined as which of the following?

• A. Thick brown lines with elevations marked at frequent intervals
• B. Thin gray lines with no labels
• C. Dotted lines
• D. Red lines with arrows

Answer: (A)

In topographic maps, contour lines show points that are the same elevation. The index contours are the bold brown lines that carry an elevation label, and they’re spaced at regular intervals (often every fifth line) to give you a quick reference for elevations across the map. This makes them the easiest way to read how high or low a location is and to gauge the terrain’s overall shape, since you can compare other, lighter contour lines to these labeled references.

The other lines are typically thinner and unlabeled, representing intermediate elevation steps. Dotted lines might indicate approximate contours or areas where elevation is not precisely defined. Red lines with arrows aren’t standard contour lines and usually represent other features like roads or boundaries, so they don’t describe elevation contours.