Contour Lines Explained
A contour line connects points that are all at the same elevation — walk along one and you neither climb nor descend, cross one and you change height. Contour lines are one of the oldest and clearest ways to show terrain shape on a flat map, and once you can read them, a topographic map tells you where it is steep, where it is flat, and where water will go.
Lines of equal elevation
A contour line connects points that are all at the same elevation. Walk along a contour and you neither climb nor descend; cross contours and you change height.
Where lines are close together the ground is steep; where they are far apart it is gentle. Closed loops are hills or depressions.
Interval and index contours
The contour interval is the elevation difference between neighbouring lines — for example every 1 m or every 5 m. A smaller interval shows more detail but a busier map.
Every fifth line is usually drawn heavier as an index contour and labelled with its elevation, so you can read heights quickly.
Generated from a DEM
Modern contours are generated from a DEM. Software follows the elevation surface and traces each contour at the chosen interval, then saves them as vectors you can edit and plot.
Because they come from the DEM, the contours match the real terrain and the interval can be tuned to the map scale.
Frequently asked questions
What is a contour line?
A contour line connects points on a map that are at the same elevation — walking along one keeps you at a constant height, while crossing contour lines means you are changing elevation.
What does it mean when contour lines are close together?
Closely spaced contour lines indicate steep terrain, while lines that are far apart show gentle slopes; closed loops represent hills or depressions.
What is a contour interval?
The contour interval is the elevation difference between adjacent contour lines, such as 1 meter or 5 meters — smaller intervals show more detail but make the map busier.
How are contour lines generated today?
Modern contours are generated from a Digital Elevation Model (DEM): software traces the elevation surface at a chosen interval and saves the result as editable vector lines that align with the actual terrain and can be adjusted for map scale.
Sources
Generate contours from a DEM in STREAM
Native Windows · fully offline · free beta