Definition
A line drawn on a chart or map connecting points of equal elevation above a fixed reference, usually mean sea level. Contour lines reveal the shape, height, and steepness of terrain: lines spaced close together indicate steep ground, while widely spaced lines indicate gentle slopes.
Plain English
A line on a map that joins all the points at the same height above sea level. Looking at how close together the lines are tells you how steep the ground is.
Context Anchor
Seen on charts and terrain depictions when a pilot is checking ground elevation along a route or near an airport.
Derivation
From the French contour, meaning 'outline' or 'shape,' which itself comes from the Latin contornare ('to round off'). On a chart, a contour line literally outlines the shape of the land at a given elevation.
Why Pilots Care
Reading contour lines correctly is essential for terrain awareness, especially in mountainous flying. Closely packed contours warn of rising ground that may exceed your altitude or aircraft performance, and they help identify ridges, valleys, and safe routing.
Analogy
Think of contour lines like rings drawn around a hill. Each ring marks one height, and the pattern of the rings shows the hill’s shape.
Intuition Check
Contour does not just mean the outside edge or general shape of something. On a chart, a contour is a specific line showing equal ground elevation.
Example Sentence 1
Before crossing the ridge, she checked the contour lines on the sectional and saw they were tightly packed, confirming a steep climb on the far side.
Example Sentence 2
Widely spaced contours showed gentle slopes that would not affect the flight path.