contour line

WordReference Random House Learner's Dictionary of American English © 2025

ˈcon•tour ˌline, n. [countable]

1. Geography a line on a map that represents the location of points at the same elevation:
   saw from the contour lines that we had several hundred more feet to climb.

WordReference Random House Unabridged Dictionary of American English © 2025

con′tour line′, 

1. Geography, Surveying, Place Names a line joining points of equal elevation on a surface.
2. Geography, Surveying the representation of such a line on a map.
3. Mathematics a line parallel to a trace. Cf. trace¹ (def. 11). Also called contour, level curve, level line. 
• 1835–45

Collins Concise English Dictionary © HarperCollins Publishers::

contour line noun

1. a line on a map or chart joining points of equal height or depth
   Often shortened to: contour