Chapter 16

Basics of Terrain & Elevation Analysis

Digital elevation models are fundamental to terrain analysis, hydrological modeling, viewshed analysis, and slope/aspect calculations.

QGIS Terrain ToolsArcGIS 3D AnalystGRASS GISWhiteboxToolsGoogle Earth Engine

Copernicus 30mBest Free DEM↗ ±4m vertical

80% of landSRTM Coverage↗ 56°S to 60°N

Theory & Foundations

DEMs represent Earth's surface as a grid of elevation values, enabling quantitative terrain characterization for engineering, environmental, and planning applications.

DEM vs DSM vs DTM: DEM is generic term. DSM (Digital Surface Model) includes buildings and trees. DTM (Digital Terrain Model) represents bare ground only. CHM = DSM - DTM (canopy height).

Free global DEMs: SRTM (30m, ±16m vertical), ASTER GDEM (30m, ±17m), ALOS World 3D (30m, ±5m), Copernicus DEM (30m, ±4m — best free option currently).

Derivatives: Slope (rate of elevation change), Aspect (direction of slope face), Hillshade (simulated shadow for visualization), Curvature (rate of slope change), Terrain Ruggedness Index (TRI).

Hydrological analysis: Fill sinks → Calculate flow direction → Accumulate flow → Delineate watersheds → Extract stream networks. All from a single DEM.

In-Depth Coverage

DEM Sources

Multiple free global DEMs available with varying accuracy.

SRTM 30m: NASA Shuttle mission, ±16m, 2000
ASTER GDEM v3: Stereo optical, ±17m, 2000–2010
ALOS World 3D: JAXA, ±5m, best for Asia
Copernicus DEM: ±4m, currently best free DEM
LiDAR DEMs: ±10cm but limited coverage

💡 Pro Tip: Use Copernicus DEM GLO-30 for new projects — best accuracy among free options.

Terrain Derivatives

DEM analysis produces multiple useful terrain variables.

Slope: Steepness in degrees or percent
Aspect: Compass direction of slope face (N/S/E/W)
Hillshade: Simulated shadow for 3D visualization
Curvature: Convex hilltops vs concave valleys
Flow accumulation: Predicts water flow paths

Key Techniques

Slope calculationAspect mappingHillshade renderingWatershed delineationViewshed analysis

Data Visualization

DEM Usage by Source (%)

Copernicus: 45%
SRTM: 30%
ALOS: 15%
LiDAR: 10%

DEM Analysis Pipeline

⬇️AcquireDownload DEM (Copernicus, SRTM)
🧹CleanFill sinks, remove artifacts
📐DeriveSlope, aspect, hillshade
🎯ApplyHydrology, visibility, suitability

Practical Workflow

Obtain DEM data (SRTM, Copernicus, LiDAR)
Check resolution and vertical accuracy
Fill sinks/depressions
Calculate slope and aspect
Generate hillshade for visualization
Perform hydrological analysis if needed
Create contour lines from DEM
Classify terrain for suitability analysis

Software & Tools

WhiteboxToolsFreeSoftware — Advanced terrain analysis

Video Tutorials

▶ DEM Analysis in QGISGeoDelta Labs · YouTube · 30 min

Real-World Application

Nepal earthquake (2015) response used SRTM DEM to identify landslide-prone slopes above villages, enabling targeted evacuation warnings.

Real-World Projects

Nepal Earthquake Landslide Assessment📍 Nepal

DEM-based landslide susceptibility mapping.

Impact: Targeted evacuation warnings for vulnerable villages.

Case Study

Copernicus DEM at 30m resolution is now considered the best freely available global DEM, replacing SRTM as the default choice for research.

Problem-Based Learning

P1 Identify flood-prone areas from elevation data alone

No flood models available. Need quick assessment for 100km river reach.

Solution: Download Copernicus DEM. Calculate Height Above Nearest Drainage (HAND) — measures each pixel's height above the nearest stream channel. HAND < 5m = high flood risk.

Copernicus DEMWhiteboxTools HANDQGIS

✅ HAND analysis identified 450 km² of flood-prone land, matching 85% of historical flood records.

Knowledge Check

1. Best free global DEM currently?