Index contour lines on a map occur how frequently?

Index contour lines on a map occur how frequently?

• A. Every fifth contour line
• B. Every tenth contour line
• C. Only the outermost line
• D. Only when marked specially

Answer: (A)

Index contour lines are the prominent, labeled lines on a topo map that provide a quick sense of elevation. They’re placed at regular intervals to let you read elevation at a glance without labeling every line. The standard convention is to have an index contour every fifth contour line. Those index lines are drawn darker and carry the elevation value, while the four lines between them are intermediate contours and are lighter and usually unlabeled. This setup lets you estimate elevations efficiently by counting lines and knowing the contour interval. So the correct frequency is every fifth contour line.

Index contour lines are the prominent, labeled lines on a topo map that provide a quick sense of elevation. They’re placed at regular intervals to let you read elevation at a glance without labeling every line. The standard convention is to have an index contour every fifth contour line. Those index lines are drawn darker and carry the elevation value, while the four lines between them are intermediate contours and are lighter and usually unlabeled. This setup lets you estimate elevations efficiently by counting lines and knowing the contour interval. So the correct frequency is every fifth contour line.