Topographic Lines
Definition
Topographic lines, or contours, connect points of equal elevation on a map, translating 3D terrain into readable 2D graphics. Their spacing reflects slope: close lines indicate steep terrain, wide spacing gentle ground. Generating contours requires clean DEMs, appropriate interval selection, and smoothing that preserves shape without creating artifacts. Index contours, labels, and depression hachures improve readability.
Application
Hikers navigate and plan routes; engineers visualize grading; planners assess visibility; and educators teach terrain interpretation. Contours remain indispensable even with shaded relief because they quantify elevation explicitly.
FAQ
How do you choose a contour interval?
Fit interval to relief and map scale—small intervals in flat areas, larger where relief is high. A rule is 10–20 lines across the main relief range for clarity.
What does the ‘V’ rule tell you about streams and ridges?
Contours form a V that points upstream when crossing valleys and a U/rounded shape along ridges—useful for rapid interpretation and QA.
How should contours be smoothed?
Apply smoothing after generation with tolerance tuned to scale; excessive smoothing shifts lines off true positions, while raw lines can look jagged.
When are depression contours necessary?
In closed basins and sinkholes, hachured depressions prevent misreading as hills, critical for flood and karst mapping.
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