contourinterval

Contour interval is the vertical distance between adjacent contour lines on a map or chart that represents points of equal elevation. It defines how much elevation is shown between lines and thus how much relief is depicted for a given area. The interval is chosen to balance readability with the level of detail needed for the map’s purpose.

The choice of contour interval depends on several factors. Map scale is a primary consideration: larger scales (more detail) typically use smaller intervals, while smaller scales (less detail) use larger intervals. Terrain relief also matters: rugged, hilly, or mountainous areas usually require smaller intervals to capture relief, whereas flat or gently rolling terrain can use larger intervals without losing essential information. The accuracy of the underlying elevation data and the intended use of the map (navigation, planning, engineering) influence the decision as well.

Contour lines connect points of equal elevation. Each line represents a fixed rise or fall relative to a datum, most commonly sea level. The elevation difference between two adjacent lines is the contour interval. Many maps label every nth line as an index contour to aid reading, with the interpolated lines remaining unlabeled.

Units are typically metric (meters) or imperial (feet). In digital terrain modeling, the interval is often selected in advance and applied across the dataset, sometimes with additional finer or coarser lines for readability. When generating contours from DEMs, the interval is a parameter that directly shapes the map’s appearance and interpretability.