Relief Shading, Hachuring & Physiographic 3D
"Techniques for simulating three-dimensional illumination and shadow across two-dimensional paper"
Before digital hillshading, cartographers used hachures—short lines drawn in the direction of steepest slope, thicker for steeper gradients (Lehmann’s Law, 1799)—or Erwin Raisz’s hand-drawn physiographic pictorial symbols.
Core Mechanism & Structure
Lambertian diffuse reflection model with standard northwest illumination (azimuth 315°, altitude 45°).
Historical Evolution & Standardization
Johann Georg Lehmann’s mathematical hachures (1799) -> Erwin Raisz landform diagrams (1930s) -> Swiss manual airbrush relief (Eduard Imhof) -> Digital elevation multi-directional hillshading.
Critical Semiotic Analysis
"Because human visual perception expects lighting from the upper left (northwest), lighting from the south causes 'relief inversion' where mountains appear as valleys and craters appear as mounds."